Mi16 1.9 rough idle

[davemar 16]

My 205 Mi16 (1.9 version running Motronic ECU, reangled standard manifold) has started to sound a bit agricultural on idle. I've attached an audio recording of it, with the mic placed behind the exhaust. The engine itself doesn't sound unusually noisy, but the lumpiness is noticeable. It sounds OK when revved as you'll hear in the recording. The roughness can also causes lots of vibrations in the car too, so I tend to give a little gas when stationary to lift it to 1500rpm or so to make it smoother and less annoying.

 

Spark plugs and distributor cap & arm all seem fine, and are relatively fresh.

 

Any ideas?

 

Exhaust_180403_mono.mp3

[jackherer 543]

It sounds like the idle mixture is wrong so check for air leaks, the hose between the AFM and the throttle body often cracks around the two take-offs and also check the oil filler cap tower and associated hoses. You can adjust the idle mixture via a screw on the outside of the AFM but it shouldn't just change by itself so look for a fault before you adjust anything,.

 

If the hoses are all OK try gently nudging the linkages on the throttle body, if it clears up when you do that the throttle body might be worn. Do the revs ever hang higher than normal when it idles? That is another sign the throttle body is wearing out.

[davemar 16]

I gave the hoses a good check over and they all seem fine. I haven't yet adjusted the idle mixture screw, and I've never needed to touch that in the past, but that's not to say it isn't playing up.