The FSM has a spec of 0.50mm maximum play for the idler arm. However, it's not particularly easy to measure this. As seen in the attached photos, you need a dial gauge, magnetic mount, and extension rod. Photos are from my 1994 E420 which had a small amount of play that could be felt by hand. At first I measured the end play at the 16mm bolt, and it was only 0.30mm. However when measuring at the end of the idler arm as shown in the FSM, the measurement increased to 1.0-1.1mm, when pressing up/down at the idler arm with fingers. This was clearly excessive, so I replaced the idler arm bushings (details on replacement are at this link). The bushings appeared original, with 155kmi and 27 years of use.
Of interest is that with the BRAND NEW idler arm bushings installed, end play at the bolt was near zero... maybe 0.01mm at most, it simply didn't budge. However at the end of the idler arm, measured movement was still ~0.30mm. This is within spec, but I expected it to be lower. The measured movement is from deflection of the new rubber bushings, when pressing up/down with your fingers. Without the dial gauge, there was NO perceptible movement at all - could not feel anything move with new bushings. It is not easy to measure only the free play without also measuring some amount of rubber deflection; you can't tell where the free play ends and deflection begins.
Bottom line - if you don't have a dial gauge setup, but can distinctly feel some free play when moving the arm by hand, there's a good chance the bushings could use replacement. However, even with the ~1mm play described above, the steering felt tight and there was no ill effects when driving. I only replaced this because the car will be going in for an alignment, and I didn't want the play to get worse after the alignment.
Of interest is that with the BRAND NEW idler arm bushings installed, end play at the bolt was near zero... maybe 0.01mm at most, it simply didn't budge. However at the end of the idler arm, measured movement was still ~0.30mm. This is within spec, but I expected it to be lower. The measured movement is from deflection of the new rubber bushings, when pressing up/down with your fingers. Without the dial gauge, there was NO perceptible movement at all - could not feel anything move with new bushings. It is not easy to measure only the free play without also measuring some amount of rubber deflection; you can't tell where the free play ends and deflection begins.
Bottom line - if you don't have a dial gauge setup, but can distinctly feel some free play when moving the arm by hand, there's a good chance the bushings could use replacement. However, even with the ~1mm play described above, the steering felt tight and there was no ill effects when driving. I only replaced this because the car will be going in for an alignment, and I didn't want the play to get worse after the alignment.
