Surging / Stumbling at Cruising Speed

[fudgitive]

Hi, I've been chasing a problem for a few months now which I thought I had solved for a while there but it's back now with vengeance and driving me nuts.

The symptoms only present themselves once the engine is fully warmed and at highway speeds, usually after 5-10 minutes of running at speeds of 125-140 km/h. The car will be happily cruising along at light constant throttle, until almost on cue, the engine will stumble and surge. The slightest adjustment of foot pressure on the pedal however will smooth it out again, and there seems to be plenty of power available even once the problem starts - only at light throttle it happens and will repeat itself until the car is parked up again to let cool, the idle however is not effected at all and I can drive normally once off of the highway as if nothing is wrong. The strange thing is, if I keep the speed below, say 120 km/h (3000 rpm ish) initially, I can drive around all day and it will not manifest itself at all.

The weather here at the moment is hot, like 40C + every day, but the cooling system in in good shape so I don't think heat is the issue, especially since it does not give trouble even when idling in traffic - only out on the highway, the temp gauge never shows any cause for concern.

I built myself a blink code reader and have been slowly working through the codes, to the point where there are no recurring codes any more apart from the temp exceeded in CAN box one (yes the blower works). The code reader, in conjunction with the meticulous records that the PO kept, have enabled me to catch up with bits and pieces that were due for replacement anyway.

So here's what has been replaced in the past 6 months -

fuel pumps / filter / relay / regulator / engine bay fuel lines
plugs / leads / coils / caps / rotors
vacuum lines
O2 / MAS / air sensors etc
EZL / cps (both) / cam sensor
radiator / hoses / thermostat / cap
stop light switch / gear select switch

The ETA and wiring looms (upper and lower) were replaced in 2006, and looms are still good under the sheathing.

The car has around 190,000km on it now.

My head is telling me ETA, but surely a new unit would last more than 5 years??

I suspect what I need to do is get somebody who can read the live data whilst the problem is showing itself, anybody else care to suggest something I've missed?

 

[Jim]

From the description I'm thinking faulty throttle pedal potentiometer...

There are some cheap dataloggers available now, Google DAQ...you could monitor the throttle body voltage and see if you can spot anything...

Jim.

 

[Cavanman]

Does it happen if you use the cruise control? It is does happen with cruise control, then perhaps it is some other issue, not the ETA. Some things that have caused stumbling/surging for me in the past (though usually at idle speeds) are

Air temperature sensor at headlight cowl disconnected (my mistake)
Air leak due to air line to purge control valve disconnected (was like that when I got it...)

With the high ambient temperatures you're experiencing it could be some other component that's breaking down under heat.

Best of luck

Cavanman

 

[fudgitive]

Does it happen if you use the cruise control? It is does happen with cruise control, then perhaps it is some other issue, not the ETA. Some things that have caused stumbling/surging for me in the past (though usually at idle speeds) are

Air temperature sensor at headlight cowl disconnected (my mistake)
Air leak due to air line to purge control valve disconnected (was like that when I got it...)

With the high ambient temperatures you're experiencing it could be some other component that's breaking down under heat.

Best of luck

Cavanman

Yes the cruise control will try to compensate for it when it is happening, nothing lights up on the dash, and it makes no difference whether the AC is on or off.

The sensor behind the headlight I replaced already, along with most of the vacuum lines under the hood, but I will recheck anyway.

 

[fudgitive]

Hmm, me thinks the problem is close to revealing itself. This morning the car had a miss right from start up, it felt like a couple of cylinders were along for the ride at times, and the surge / stumble / miss whatever you want to call it, is present right through the rev range. Shut down and restart makes no difference. The weather was not too hot this morning either, only 34C but perhaps a little on the humid side. Confirmed that the cruise control does work, but the miss is still there when the cruise is on and I can feel the cruise control compensating for it. The idle is as smooth as silk, I did lift the hood before shutting it down when I arrived just now, pulled the vacuum line off the EZL and the idle surged then settled back down almost immediately, strong vacuum at idle at least. Will check for codes again after work and see if anything has popped up. It has not gone into limp home mode as yet.

I removed the modules on the weekend, cracked open the E-Gas and LH modules (looked like they had never been opened before) to look for any obvious signs of component failure... there was a slight dark spot on the plastic board cover of the LH module where the cover had obviously been exposed to excessive heat over one of the surface mounted resistors - but I figure after 20 odd years one might expect that, so didn't delve any further (nor do I have the skills to dissect a module).

Is module failure common in hot climates?

With a miss that bad, I would expect to at least smell fuel if the problem was ignition related, so I am leaning towards suspecting a fueling issue.

Anyway highly likely that I will be stuck on the side of the road sometime this week, at which point the problem will be obvious I hope !!

 

[fudgitive]

OK Just rechecked the codes on all modules, I get :

Pin #6 ABS+ASR = 30 CAN data bus to EA/CC/ISC interrupted
Pin #7 EA/CC/ISC = 14 closed throttle switch
Pin #8 Base Module = 5 temp in CAN box exceeded, and 6 A/C clutch jammed or poly belt broken

Only one of those codes bothers me, the first one ! The second code was me blipping the throttle from the engine bay the other day, the CAN box temp code always appears, and the A/C clutch poly belt one I drove through a puddle on the weekend and the compressor cut out, restarted the car and it was fine after that so I think just the belt slipping for a few minutes. Could the first code on the ASR module be in any way related to my ASR defeat switch (I don't see why as it has never thrown this code before)???

I noticed that the new cam sensor is weeping a bit from the o-ring so am going to pop the dizzy caps off now and double check their condition - they are 2 months old Bosch so should be good I would think.

>>>>OK checked caps and rotors, like new. Measured battery voltage 12.6v with the car off, and 13.8v running under load. Cleared the codes and will see what happens next>>>>

 

[Cavanman]

I've seen the CAN bus error on my own car. That was just when checking for error codes rather than a running problem so I don't think it's anything to be too worried about unless it keeps recurring after clearing down the codes.

Could it be a distributor cap? Here in Ireland the problem I had was moisture seeping into a cracked distributor cap. the symptoms were somewhat unusual.

From cold it would start and run fine. After about 3 miles, if I slowed down, the car would start to miss badly; basically I think 4 cylinders were not firing. Switch off, wait for about 10 minutes for heat soak to dry out the moisture, start up and then it would not miss a beat after that.

I think that the reason for the 3 miles was that the EZL was reacting to engine temperature, changing the dwell time or some other parameter, which resulting in a differently timed or different spark which could no longer overcome the moisture in the crack.

While I suspect it's not moisture that the problem for you it might be worth removing the caps and giving them a wipe to clear any carbon tracks etc.

 

[gsxr]

Long shot - the insulators behind the distributor caps, as referenced here?
http://www.w124performance.com/docs/mb/other/ignition_misfiring_STAR.pdf

 

[gerryvz]

Long shot - the insulators behind the distributor caps, as referenced here?
http://www.w124performance.com/docs/mb/other/ignition_misfiring_STAR.pdf

That's a very illuminating article Dave. Where in tarnation did you find that, anyway?!?

 

[gsxr]

That's a very illuminating article Dave. Where in tarnation did you find that, anyway?!?

I think it was from a Baidu search engine! They have the most interesting stuff there....

 

[gerryvz]

百度 That article is the answer to a lot of folks' prayers. If you have anything more like that, by all means please post it !!

 

[fudgitive]

Long shot - the insulators behind the distributor caps, as referenced here?
http://www.w124performance.com/docs/mb/other/ignition_misfiring_STAR.pdf

Actually the ignition system work was done by the workshop that I normally use, not by me. I recall that they made me wait an extra day for a suppressor housing to arrive from somewhere, as one was broken, but I am not sure whether these insulators were replaced - they did the caps, rotors, leads and plugs at once along with the suppressor housings.... hmm I was hassling them for the car back so there is always the chance they overlooked them. Lol never been happy with the way they laced the wires so now's my chance to make it all look pretty I guess. I pulled the caps last night, are those insulators always orange because the ones fitted look black to me ?? Number 14 in the attached diagram right?

Oh on a side note, Lemforder engine mounts purchased from Autohaus earlier this year, 15,000 km and one of them is toast already !!!

 

[gerryvz]

on a side note, Lemforder engine mounts purchased from Autohaus earlier this year, 15,000 km and one of them is toast already !!!

Not a surprise, Fudge. Lemforder is on my "do not buy ... never put on my car" list and in my book is about equivalent with Meyle parts. Thanks for the update on this. Good luck with your running problems.

 

[fudgitive]

Well I checked the Insulator on one side just now, and it is indeed a new piece which means it should be a genuine part - it is black though with an orange o-ring... the allen bolt holding the bracket was proving to be a potential cause for tears, so I left it alone for now and am assuming new part so should be good. Come to think of it the same problem was occurring even before they did all the ignition work, what makes the problem so much more noticeable now is that the car is running great apart from this one niggling thing, after changing all the other overdue bits.

A few random irrelevant off topic out of focus overhead shots of this afternoons warehouse adventure.... and we really need to stop buying stage because pretty soon there will be no space for my after hours tinkering any more !

:sad:

 

[gerryvz]

Fudge ... it looks like your top radiator hose (from the bends in it) may not be a factory hose, so may be rubbing against your PS reservoir. Just a quick observation.... The factory hoses are more parallel to the back side of the fan shroud and thus provide adequate clearance and don't rub.

Cheers,
Gerry

 

[gsxr]

Agreed. Here is a photo of the correct / OE hose:

 

[fudgitive]

Duly noted on the radiator hose.... back to the insulators, so item #14 in the diagram further up the post, is that just the dust cover, or is that actually the insulator?? Does the insulator come with that cover as the optional part on the EPC? Bit confused as I did not manage to crack the allen head holding it all on this afternoon, so have not really seen the component parts.

 

[gsxr]

#14 is the insulator, which also acts as a (rear) dust cover. It sits loosely behind the rotor, you need to remove the rotor and rotor bracket and then the insulator just pulls out.

 

[fudgitive]

Ah so that is the bit I was looking at, I got as far as the rotor bracket but the last bolt holding it in wouldn't budge and I didn't trust my allen key - anyway it looks to be a new part. Thanks for the clarification.

 

[fudgitive]

.

Anyway highly likely that I will be stuck on the side of the road sometime this week, at which point the problem will be obvious I hope !!

Well the car finally stopped on the way home from work today..... well almost anyway !

I had just about reached home, 20 minutes into the drive with outside temp just a tad under 40C, the stumbling had already started at the usual spot a few miles back down the road so I was trying to vary the throttle load a bit to avoid the miss, which has been getting progressively worse - I think the power has been down a bit the past few days also, along with the engine mount vibration it made for a most unpleasant drive home.

So I took the motorway off ramp which is a gentle right hander followed by a tighter left, as the car entered the left hand turn, at about 80-90km/h, the engine started to miss and then stopped all together - I thought the car had stalled actually because the throttle did nothing, so coasted it around the off ramp down to the flat where there was a safe place to stop. Dohh, the AC brakes and power steering were all still working so it hadn't stalled, and only after I pulled up I realised that the engine was sitting in a fast idle - 1100 rpm.... here's the thing, the throttle did nothing, foot flat to the boards either in gear or park, nada ! No dash lights, all of the gauges showing what they should be, and idling smoothly at 1100 rpm. Hmm.

Engine off, restart and all working again.

Letting it cool down at the moment, then I will go down and recheck for codes.

With the motor mount shot, there would be more engine movement, especially at speed around a bend, possibly exacerbating a harness problem??? .... might pay to have a closer look at the wiring that I thought was all good.

 

[fudgitive]

Codes checked, #30 on pin 6 has come back again, and a new one has appeared code #3 on pin 7. No other faults on any modules.

 

[gsxr]

#3 on pin 7 (ETA) is indicating a fault with the ETA internally. When the ETA was replaced in 2006, was it a brand-new unit, used, or rebuilt? I'm thinking you likely have a faulty ETA.

BTW - you can pretty much ignore code 30 on pin 6, this is a generic fault that often appears with other fault codes.

 

[fudgitive]

Oh I dug out the receipt finally (the cleaning fairies have moved all my papers AGAIN!) and I was a year out, he purchased A0001417925 on the 8th of May 2005, and paid AED 3080 ($840) for it, so must have been a new part me thinks.... so that's 6 and a bit years. The current price I got online 956 Euro, will see what my local parts shop can offer tomorrow.

 

[fudgitive]

Bit of an update, I went to buy some brake pads this morning and thought I would ask what price the ETA (A0001417925) would be from my local MB parts supplier, imagine my surprise when he punched in the number and they happened to have one sitting on a dusty shelf out the back.... list price $2314 (ouch). I showed him the online price from Germany which is currently $1367, then I had a moan about the condition of the box that it was in, and he offered it to me for $1157, so I grabbed it along with a gasket and the vacuum pipe that I will no doubt break in the process, and a tube of MB gasket sealant. I noticed that parts.com have the price at $1002, but shipping to Dubai would have made that more expensive than the local guys anyway.

Today I'll do the brake pads and wear sensors, tomorrow enshalla the ETA - I'm 99% sure that it will cure my problem, but I guess if it doesn't then I've got a spare. There goes my beer and skittles coin for this month!



The box is dated June 2001, and it's VDO.... LOL I wonder if the wiring loom has degraded before it's even put on the car ?

 

[fudgitive]

Well, what an unpleasant task that was.

I am pleased to say however, that the car is running 100% better already, and I'm hoping that with some fresh oil and an Italian tune up tomorrow, she'll be going like a train.

Once again, the internet proved a useful thing, especially for little tips like tying something to the spring that attaches to the linkage on the side of the ETA, the other end of which seems to attach in the depths of darkness under the inlet manifold somewhere, and attaching the gasket to the ETA with some sealant to keep it in place whilst the unit is jostled into position, helped a lot.

The most difficult part for me was getting the old one out, the 4 attaching bolts didn't want to budge so I had to let them soak for a while until they eventually yielded. Tried every attack angle to get the bloody thing out from the manifold without success, so I wandered off for a coffee and came back to it with a fresh resolve an hour later - hand straight through the air flap with fingers grasping the underneath of the ETA like a handle, flip it up 90 degrees, and it came straight out! The new one went in just as easily, little bit of fussing around lining the gasket up properly but not difficult.

Wow, it must have been running like a dog before because it is like night and day between the two ETA's... WooHOO !!

 

[fudgitive]

After a couple of days driving around, I can confirm that the problem has been completely eliminated by replacing the ETA, thanks for the advice guys.

 

[Silver Arrow]

Well done!

So what was WRONG with your ETA?

And why could it not be repaired?

 

[fudgitive]

Well done!

So what was WRONG with your ETA?

And why could it not be repaired?

Good question.... the old one is still a greasy thing in a cardboard box at the moment, eventually I'll clean it up and have a closer look, it may well be repairable. Having the car off the road for a week trying to get the old one fixed was not really an option, since it's my main mode of transport and would have had to rent something else in the mean time, made more sense just to buy a new one and then keep the old one as a spare if it is indeed repairable.

 

[195910]

Hi,

Good to hear you got it sorted, But May I ask what the total cost was for all the parts replaced? From the list in the first post and now the ETA, I am guessing $5000 over 6 month...Ouch.

But the good news its done.. now its driving time!

 

[fudgitive]

Plus tyres, rims, brakes, ice, paint etc. Your guess is probably right, will have to go through the receipts and add it all up. The thing is it's also a hobby for me, and even if I've spent say $15000 including initial purchase, what could I have bought new for that price that would even come close to offering the same driving experience? I've put over 20,000km on the car in that time also.

 

[Silver Arrow]

Plus tyres, rims, brakes, ice, paint etc. Your guess is probably right, will have to go through the receipts and add it all up. The thing is it's also a hobby for me, and even if I've spent say $15000 including initial purchase, what could I have bought new for that price that would even come close to offering the same driving experience? I've put over 20,000km on the car in that time also.

Agreed. The value for money is definitely there. That same $15,000 won't even buy you a new Honda Civic. To me it's about the ownership and driving experience. You have in your garage what was effectively an exclusive near-supercar, a limited edition handbuilt special from two of the world's finest marques working together. It's a highway beast sculpted out of granite. For $15,000, which nowadays for a similarly-sized 4-door sedan that performs is a pittance.

 

[195910]

absolutely, the most basic/cheap cars now are so expensive, that whatever amount spent on older high end vehicle is worth it.
Civic's and Hyundai's are now alot more than $15K

From my experience, and for my future 036. I am going to get a well preserved and fully MB documented example out of the original owner... although I only spent a total of about $7K in 7 years on my car (including all the Cooling and A/C mods), still I think an even better example would have provided an even experience. And the Extra $$$$ in the purchase price would have paid it self off.

 

[fudgitive]

Well done!

So what was WRONG with your ETA?

And why could it not be repaired?

I cleaned up the old ETA and pulled it apart to try and see any problems. What I discovered is that it must have been a rebuilt (or at least rewired) unit, as the flying lead wires appear to have been re-soldered to the PCB and are all still in good condition. There was also excess sealant applied to the old gasket, so somebody had certainly been there before.

However on the side where the pot is, that had never been opened before as the check pin was still intact, can't really see anything obvious and the resistance of the pot is smooth and linear across its movement... of course it was only giving a problem when the engine was hot, so the pot is still the likely suspect I guess.

 

[DarkStar]

I've been struggling with something similiar.
I notice a surging/stumbling at cruising speed (no load, hi vac)....thought it was the transmission but realized after testing while parked it
was the engine. Think it could be ETA.

With car in park, light pressure on throttle just up off idle (trying to hold a steady, barely open throttle), it stumbles at 1400rpm and drops back to 1000rpm. If I accellerate a bit harder (29-30seconds into the video), the car is flawless, pulls strong. Thought it was the EGR but disconnect that. I have replaced most (all?) of the vac lines and elbows.

I don't have a code reader, gonna build one this weekend.

I made a video of it...

http://www.youtube.com/watch?v=JisG0kbbFtg&feature=youtube_gdata_player