Poor Idle tried lots of different things still no joy.

[J_A_R_B]

I have recently just rebuilt the head on my 87 325i sport e30 new cambelt etc...it starts ok etc but after about a 30seconds to a couple of minutes the engine starts running badly missing and juddering. When raising the revs it no longer is a problem.

Driving seems ok although there are a few flat spots and when pull up with window open can smell unburnt fuel. Also noticed that when coming upto lights and drop clutch say in 3rd the engine will sometimes stall.

I have cleaned the ICV and checked the resistances on terminals. 40 ohms terminal 1&3 and 20 Ohms on terminals 1&2 and 2&3.
I have also checked the blue sensor which was returning values specified in the haynes manual.
I have removed the TPS cleaned it and checked for continuity on terminals 1&2 which is fine but on terminals 2&3 and throttle is close to fully open don't get continuity but do when test within TPS (split in half) seems to be break where terminals are molded into plastic and travel to socket. Would this make a difference to idle?

I have cleaned the AFM and checked the resistance values when moving the metal flap which goes up smoothly.
When checking the sensor that comes from AFM housing resistance raises with breathing hot air on the sensor.

I have also tried removing TPS connector which made no difference to idle.
When removing the AFM connector sometimes will stall but when doesn't stall revs raise slightly and idles smoothes out and all seems ok (thought at idle AFM did nothing)

I have tried spraying Carb cleaner around manifold to find a potential leak but no joy.

The car does idle quite low around 650 rpm to 700 rpm. I haven't checked the Plug gapping (put new NGKs in after rebuild).

Having cleaned the TPS and AFM this evening went for drive and throttle response seemed better and car seemed to be running better although idle is still bad but didn't stall when in high gear and drop clutch.

I believe I have tested most things but am at wits end to what the problem is.

Any Advice would be massively appreciated,

Regards

James

[dMh]

have you adjusted the throttle stopper bolt on the engine? (the thing that links to the throttle cable)

you could also have a loose cambelt, i've had this problem before and i think its either that or the throttle stopper. although it could also be the spring tension on your AFM.

[J_A_R_B]

dMh do you mean the adjuster that will raise and lower the idle depending on which way you turn it? How does the cambelt being loose make a difference (unless its slipping) if anything felt tighter than old belt. This is really getting frustrating now

[DaveD]

did you put a new gasket on the throttle body when rebuilding as I forgot on mine and had similar problems

[dMh]

yes i do mean the adjuster, try to adjust it to see if thats where the problem is.

as for the cambelt:
well a week ago i had a problem with my car, it won't start, it turns out my ignition and fuel pump relays were bad (i also ended up changing my TPS).

i also found out that my cambelt was loose, so whenever i tried to rev the engine up it would judder and heavily hesitates, sometimes it would also give out a VOOMP sound from the engine (or the exhaust, hard to know since its quite loud) as if a wind is shooting back.

so i asked my mechanic to tighten the belt and voila, problem solved. i think because the camgears and eventually the valves were not in sync properly with the crank it made the judder, hence the cambelt can jump a gear or two on the camgear if its loose.

[J_A_R_B]

Dave D

No but the TB wasn't taken off until last night when cleaned TPS and AFM. I will be putting a new gasket on the TB once I have sourced a new TPS to rectify the problem with contiuity when throttle is open (8 to 12 degrees from fully open). I am pretty certain its not the Gasket as sprayed around with Carb cleaner and no change in revs.

dMh

Reving the engine is not a problem just the idle is bad. Only slight incling of problem is when removing AFM connector problem goes away but many people say AFM does nothing at Idle but a few say it does.

I really don't want to get into replacing everything without knowing if there is a problem.

[Brianmoooore]

If unplugging the TPS makes no difference to your poor idle, then there's a good chance that the TPS is the problem.
DO NOT touch the throttle stop on the throttle body. The idle speed on an E30 is controlled by the ECU and is not adjustable without software changes. The throttle stop is factory set, and needs special equipment to adjust properly!
AFM signal is not used at idle, UNLESS it is giving an output that is not consistent with idle, in which case the ECU seems to get confused..

[J_A_R_B]

Thanks Brian

Doesn't make sense to me what you are saying. I would have thought the TPS although faulty on one of continuity tests the one that was fine was the micro switch one (terminal 2&18 ) so until going full throttle would have thought the TPS wouldn't be causing a problem as with the TB closed the switch is closed therefore telling the ECU the the car is on idle. Voltages on the connector were also the correct 5v.
Can you advise why the idle would smooth on removing the AFM? Would the TPS effect fueling? As its running very rich and see grey smoke out the exhaust.

Thanks all for your suggestion so far.

James

[georgen]

Thanks Brian

Doesn't make sense to me what you are saying. I would have thought the TPS although faulty on one of continuity tests the one that was fine was the micro switch one (terminal 2&18 ) so until going full throttle would have thought the TPS wouldn't be causing a problem as with the TB closed the switch is closed therefore telling the ECU the the car is on idle. Voltages on the connector were also the correct 5v.
Can you advise why the idle would smooth on removing the AFM? Would the TPS effect fueling? As its running very rich and see grey smoke out the exhaust.

Thanks all for your suggestion so far.

James

I'm sure that you've tried this already, but have you checked all air hoses for splits and / or slackness ?

[J_A_R_B]

Yeah have indeed also sprayed them tonight with carb cleaner in order to find leak but no joy.

[dMh]

well Brian, that's odd, the idle on my car is very adjustable from the throttle stop, i find that the idle always follow the throttle stop whenever i changed it (and with no problem whatsoever), mine is an M40 btw, don't know if that makes a difference as i've heard that the motronic ECU on my engine only deals with supplying air and fuel to the engine and not the idle itself, although it does monitor the idle to give the correct AFR and spark timing...

but i haven't heard that it actually controls the idle before. interesting...

[Brianmoooore]

The Motronic ECU on an M40 has sole control of the idle speed.
If the throttle stop has been adjusted inwards or the throttle cable is too tight then either of these will override the ECU's control of the idle, since the ECU cannot reduce the idle speed below the level set by the amount of opening of the main throttle plate. Your car needs everything on the throttle body set up from scratch, or the TB replaced to give your car a chance of running properly!

[dMh]

hmm, I see... well, that's new to me... thanks!