240
After leaving home this morning, I shifted into 3rd gear, let the clutch out, and nothing happened for a few seconds. Then with a bit of a jolt, the power kicked in and all was normal.
Then I slowed down to turn at an intersection, shifted into 2nd, and the car just no power whatsoever (it wasn't just down on power - there was nothing at all).
Came to a stop, moved off in 1st, and all was good - except for the idle, which was very odd. Sitting at the lights, the revs would drop to about 1100, then surge up to about 2000, then repeat over and over - without me going anywhere near the throttle.
I can tell that it was trying to do the same thing when I was actually driving - I sat at 40kmh in 3rd, and without me touching the throttle, my speed gradually increased to 45kmh.
Then this afternoon, a similar thing happened again - moved off from the lights in 1st, there was some violent jolting with the power cutting in and out, then nothing at all for a few seconds - then back to normal.
As a bit of background - not sure if it's relevant or not - for a while the car has had an issue where it would not immediately fall back to the standard 900rpm at idle. ie, I'd come up to a set of lights and stop, the revs would stay at about 2000 for a few seconds, then drop back to 900.
It's a 1992 240, B230FX, LH 2.4.
Thanks!
jamesinc
So hunting idle seems to be the theme.
I'd start by looking for significant vac leaks (the intake flex hose is a prime culprit) and testing idle with the AMM connected and disconnected.
The not returning to idle issue could be a stuck ICV, and it could also be a missing speed signal to the ECU.
Also check your throttle position sensor is set correctly. If you open the throttle by hand, you should hear the microswitch in the sensor click as soon as the throttle plate starts moving.
As usual with LH-2.4 the best debugging method is to disconnect/reconnect sensors to find which one is upsetting the system.
240
Thanks for the pointers James. I was definitely going to try disconnecting the AMM, hadn't thought of the throttle position sensor though.
I did suspect the ICV too, but not sure how to diagnose that without just replacing it...
There is one vacuum leak that I know of, as my vacuum (fuel consumption) gauge has a crack in it - but it's been like that for a few months, and it's only been this bad the past couple of days.
I did pull a faulty AMM code from the diagnostics box about 6 months ago; it never came back after I cleared it but I guess that indicates it could be on the way out.
jamesinc
240;129532 wroteI did suspect the ICV too, but not sure how to diagnose that without just replacing it...
Just unplug it, you should immediately notice a difference and high idle.
lasercowboy
+1 for a vac leak, if it's hunting for idle.
If it just hesitates/stutters then you suddenly get power again, fuel pump fuse/wiring.
240
So to be honest I never really addressed this, as the car ran fine 99% of the time - all that has happened for the past couple of months is that the idle has been a little high, and occasionally (about once a week) it does some weird idle revving behaviour where it would rev up to about 2500, then back down to about 1000, then do that over and over. If I restarted the car it was fine.
But this evening, after driving about 500m it started 'hunting' for revs - it would almost stall, then get a little bit of power, then go close to stalling again. I restarted the car a few times and it actually got wore, to the point where it stalled as soon as I started it.
I read the codes from the LH2.4 diagnostic box in the engine bay and it gave me 1-2-1, "AMM signal faulty or missing".
After doing that (would have been about 5 mins) I started the car again and it was fine.
The only other issue I can think of that may be relevant is I can hear a bit of a vacuum leak, but haven't been able to trace it yet.
Is it possible that the vacuum leak is causing that AMM code, or could a bad AMM cause this behaviour?
lasercowboy
Find/fix the vac leak first, then worry elsewhere. Otherwise you'll end up 'fixing' things that don't address the underlying problem.
240
I've got to find the leak first!
Spraying around the engine with it idling, the revs varied slightly when I sprayed around a couple of the injectors. Do injector seals count as a vacuum leak?
I can hear a 'hissing' sound too, not sure if injector seals would cause that?
Vee_Que
It will be a combination, but 25 year old seals will fail.
240
Yeah I think I have a spare set of seals so I should probably just do them anyway...
But I guess a 25 year old AMM is likely to fail too
Ravanelli
Disconnect the ICV and give it a good spray with throttle body cleaner. They can get clogged and it causes crazy idle conditions. Replace with a good spare if you have one to test. Quick and easy job
240
I thought the ICV had to be replaced and couldn't be cleaned? But if it can be cleaned I'll definitely give that a go.