What controlls idle on these cars other than the ETA?

[Ascension]

Mine is a non ASR 95 E420. I have an intermittent idle surging issue in gear. Pop it into neutral or park is rock steady at around 750 RPM but will surge so badly it almost dies then will react catch and rev at times in gear. Yesterday was the worst it has ever been and I had an audible buzzing from the eta at times as it reacted. Cruse function is rock steady and the car idles at around 750 out of gear. If an ASR car the way it's acting would suspect bad EGAS or ETA but from what i understand a bad ETA on a non ASR car will not react like this and don't have an Egas so?? Upper harness and ETA were both updated last year.
Got home late yesterday and have incoming storms here so have not pulled codes yet.

 

[gerryvz]

Sounds to me like a vacuum leak.

 

[gsxr]

Idle speed is controlled by ETA and, for non-ASR cars, the T/LLR module.

Gerry is right, a vacuum leak (including PCV system) can cause idle issues.

 

[Ascension]

Sounds to me like a vacuum leak.

First thing I thought also but if it's there I so far can't find it And trust me i have looked with the car both running and not + listened! May smoke the system as that is the only thing left I have not done on the vacuum side.
Problem is intermittent some times it's perfect. Pop it out of gear idles at 750 rock solid in gear 500 and the same then it will suddenly start running up and down. Yesterday there was a change as when it was really acting up you could hear an audible hum from the ETA. It was like the controls were sending a wide open signal to the ETA forcing the throttle plate closed then releasing just as it was about to die causing it to catch and rev.. Snap it out of gear and idle returns to a rock steady smooth 750 or so RPM so??
On a non ASR car the throttle is all mechanical and the plate is open at rest with a spring load the signal from the T/LLR causes the plate to close slightly in order to regulate idle speed which is completely backwards to how it works on an ASR car. If you have a bad ETA a non ASR car will idle high normally and the cruse will not function not drop idle speed like this one is doing.
[video=youtube;oluUNq4Yznc]https://www.youtube.com/watch?v=oluUNq4Yznc&t=302s[/video]
One of the little things that are different between a non ASR 400 or 420 and a 500 or 420/400 with the optional ASR.

 

[Ascension]

Idle speed is controlled by ETA and, for non-ASR cars, the T/LLR module.

Gerry is right, a vacuum leak (including PCV system) can cause idle issues.

Specific question on this bro. Would a vacuum leak not result in a HIGH idle and not the surging low idle issue I have in gear?? Once off idle car runs fine and throttle response so far is crisp. Today is a nice day so about to dive into the car. 1st thing is take a look just for thrills and giggles at the caps rotors and in particular those insulators as i dried mine off last year sprayed them down and reused um. Just want to eliminate that first as a potential issue with all the hot cold and monsoon rain we have had this year.

 

[gsxr]

I think it depends on the size of the vacuum leak. From memory, one of my cars would have a significantly surging idle in gear, when the 8mm PCV tube was open to atmosphere (the one which connects to the purge valve next to the EZL). It will drive fine like this but the idle can be pretty terrible.

Caps/rotors/insulators cause misfires, generally not surging.

 

[gerryvz]

The surging is likely because the system is continually trying to compensate for the leak.

Your only fix on this is to check/remove/replace all vacuum lines, valves and hoses relating to the top end of the engine.

 

[emerydc8]

Mine is a non ASR 95 E420. I have an intermittent idle surging issue in gear. Pop it into neutral or park is rock steady at around 750 RPM but will surge so badly it almost dies then will react catch and rev at times in gear.

FWIW, I had a similar problem once with a 93 400E (non-ASR), except it would surge when in reverse. It turned out to be a bad neutral safety switch.

 

[Ascension]

Forgot about this thread. Turned out to be a bad TLLR module in the end.