E30 Idle Problems

[duvey 245]

I've been hunting for a fix for my chunky idle ever since I swapped in the new engine. Other than the idle speed the engine seems to run well.

It idles around 600rpm. If you rev it then throttle off it will dive to around 500rpm on the way down before recovering.

It seems to idle worse when cold than warm.

Temp gauge usually reads a a bit too cold unless it is sitting and idling.

So far I've replaced (to no avail)

dizzy cap and rotor

spark plugs (old ones maybe a bit on the white side of normal?)

a cracked valve cover breather hose

blue & brown temp sensors

thermostat

I have reason to believe the throttle body set screw has been f*cked with. I've reset it using a feeler gauge and have made sure that the TPS is getting continuity in the closed position. Interestingly no continuity (on the other pin) when fully open, from what I've read this is wrong, but shouldn't effect idle.

I've sprayed around with carb cleaner on the intake side and idle didn't change. I've inspected everything fairly closely and can't see where there'd be any vacuum leaks.

If you take the oil cap off while running it will very nearly stall.

Any suggestions on a next step? Kinda doing my head in.

Cheers guys

Edited November 8, 2015 by duvey

[_ethrty-Andy_ 2122]

what about the idle control valve

[RLK 0]

Try leaning off the idle mixture. It s an internal hex headed adjuster on the top of the airflow meter, sometimes hidden by a blue blanking plug.. CCW to lean off the mixture .Try half a turn then rev the engine and let it return to idle. when the idle mixture is correct the engine should drop straight back to a steady idle without dropping too far and then recovering.

[duvey 245]

Re: ICV, I've tested with a multimeter - reading correct 40ohms over outer two pins and 20 ohms over inner and outer pins. Thanks for that Ross, will take a look now.

[will 169]

Try leaning off the idle mixture. It s an internal hex headed adjuster on the top of the airflow meter, sometimes hidden by a blue blanking plug.. CCW to lean off the mixture .Try half a turn then rev the engine and let it return to idle. when the idle mixture is correct the engine should drop straight back to a steady idle without dropping too far and then recovering.

Really?

[hotwire 352]

Really?

Yep, my thoughts exactly

[duvey 245]

Yep, my thoughts exactly

Out of interest, anyone know what the internal hex under the blue blanking plug is actually doing - mechanically speaking?

[alisterh 26]

Out of interest, anyone know what the internal hex under the blue blanking plug is actually doing - mechanically speaking?

Bypassing the afm I believe

[duvey 245]

Bypassing the afm I believe

Had a fiddle (making sure i kept the original registration position to go back to). Might have made some slight differences but nothing really noticeable. Still definitely idling too low.

[duvey 245]

Confirmed yesterday that the cold running issue isn't being caused by a stuck open thermostat. Anything else I haven't ticked off here?

[nick496 268]

Here's a pretty comprehensive list: http://www.e30tech.com/forum/showthread.php?t=3272

Doesn't tell you how to test them, but hey you can google them all

[_ethrty-Andy_ 2122]

resistance of the ICV wont tell you if its jammed shut, not alowing to open correctly, slow to respond etc. you have diagnosed its not an electrical failure of it, but could be mechanical failure.

[actletpone 43]

I was of the understanding screw on AFM should not be touched without co meter and is only there for factory idle mixture setting. Any fix you achieve by adjusting it is most likely a band-aid fix unless it has been messed with before?

Most guaranteed way to eliminate intake leaks is smoke test.

Does the idle raise when aircon is turned on?

Fuel pressure? Injectors or c191 plug connections. AFM can be checked with multimeter also.

[duvey 245]

I was of the understanding screw on AFM should not be touched without co meter and is only there for factory idle mixture setting. Any fix you achieve by adjusting it is most likely a band-aid fix unless it has been messed with before?

Most guaranteed way to eliminate intake leaks is smoke test.

Does the idle raise when aircon is turned on?

Fuel pressure? Injectors or c191 plug connections. AFM can be checked with multimeter also.

Cheers.

Has no A/C, but I have a few other things to try. Will report back.