Idle valve issue?

[NigelA]

1979. 325iT. Was running fine. Then it wouldn't start. Cleaned the ICV carb cleaner and re-fitted. Engine ticked over fine - for about 15-30seconds, then went to 2000RPM. Cleaned another ICV and put that on with the same result. Same with a third one. Have checked for vacum leaks; can't find any. What's happening and what's he solution please?
Thanks in advance for any helpful advice.

[Mikey_Boy]

Have a quick search for this topic - this could be a Throttle Position Sensor problem...

[NigelA]

Many thanks, Mikey. Will do that.

[Grrrmachine]

Can you confirm the engine? I didn't know there was a turbo 325i...

[NigelA]

Hi Grrrmachine. Possible confusion here. 325iT is the Touring, not a turbo.

[NigelA]

Mikey_Boy. There is nothing coming up on the forum regarding TPS. Haynes manual has it. Could it be a case of applying carb cleaner to the main air flow housing (where the TPS) is? In other words, like the ICV does it need cleaning an lubricating?

[Mikey_Boy]

Darn it - I tried the serach and got nothing...!

Couple of things to try - check the resistance of your idle speed control valve. Across the 2 outer pins the resistance should be 40 Ohms - between pins 1 and 2, 20 Ohms and the same for pins 2 and 3. If the resistance is different then the idle valve is dead and needs replacing.

The throttle position sensor is under the throttle body and has 3 settings - idle, part load and full load. If you open and close the the throttle near to idle, you should hear a 'click' as the TPS goes closed - if you don't then you need to have a look at your TPS function - moew explanation here:

http://forums.bimmerforums.com/forum/sh ... ?t=1686284

(I know, I know, another forum...)

Also, have a good look around for air leaks - I know you have checked this, but have another look - there are loads of places for air to leak through causing high idle speed, including the inlet manifold itself (when I had similar problems, it was a loose intake manifold causing issues - easily solved!)

Good luck...

[NigelA]

Many thanks, Mikey. Much appreciate your input. Will run through those options

[NigelA]

Have checked the resistance on the ICV contact, and also on the TPS contacts in the two recommended throttle positions. All looks good there. Also check checked for air/vacum leaks - wriggles the hoses and rubber tubes in various places but not change in engine note. Also replaced the ptfe tape where the ICV feeds into the air intake.
Started the car, from cold. ran at normal tickover for perhaps a minute to a minute and a half and then went to 1500 RPM and stayed there - again wriggling hoses etc made no difference.

Could this be the TPS moving out of position for some reason?

Any further help or comments would be appreciated.

[Mikey_Boy]

Here's the thread I was looking for:

http://www.e30zone.net/modules.php?name ... c&t=153524



I would check your TPS back at the ECU pins - all very well having a TPS that works (are you 100% sure?) but that means nothing if the signal isn't getting to the ECU...

Also, try the trusted method of using WD40 or carb cleaner to detect air leaks...

Final thought is your one way valve going to the brake servo... If that's foobar'd, it can cause idle issues...

[Mikey_Boy]

Have you also checked to see if you inlet manfold is tight? Mine wasn't and it caused all sorts of havoc - rough running cold, better as it warmed up and then rough as a badgers bottom when hot...

[Mikey_Boy]

And last up - might be worth checking the Idle valve resistances when the car is HOT - it's not unknown for these units to behave when cold and then break down when hot...

[Mikey_Boy]

And really finally - have you checked your water temp sensor resistance??? That could also cause problems... This should be 2000+ ohms cold, 360ish warm.

[NigelA]

Many thanks, Mikey, for the help and trouble you have taken. Have printed out the Motronic 1.0 info and will work with that and your other suggestions.

[NigelA]

Went as far as I could go without removing the throttle body (need a gasket for that). The TPS, on resistance, shows the right values at the different openings but, only 'clicks' when just opening or, about to close, so maybe that needs to be removed and cleaned.

The voltages across input to the ICV are 8.8 and 3.75 where they should be 10 and 5. Don't know whether that variation is significant.

On the last start-up ticked over normally initially (about 600 RPM) then went to 1500 for a while and then slid gradually back to around 800. Opening the throttle gently causes engine to splutter before picking up revs. Disconnecting the ICV at 1500 RPM caused no change in revs and at 800 RPM caused a perceptible change, but not much.

Any further comments anyone please? Any many thanks for all the help so far.

[Grrrmachine]

1) Sorry for the confusion. "1979 325iT" didn't sound like any E30 I'd ever heard of.

2) Your engine is an M20, and these are known for idling issues but usually erratic rather then high ones. I fear Mikey_Boy's led you on a bit of a wild goose chase though. If your car is 1989 like your sig, it will have Motronic 1.3 instead of 1.0.

3) Your TPS SHOULD click as soon as the throttle arm moves away from rest or returning to that position.

4) Have you had the battery disconnected at any point recently? The ECU is a (primitive) learning ECU, and if the battery has gone flat then it will lose its mixture settings. When restarted, it will idle high and run rich for a while until it's relearned its settings. A 10-minute idle session followed by a good thrash normally sorts it out.

5) Other things to look at are a loose connection to the AFM (which results in high idle and poor throttle response), a loose connection to the Blue Temp Sensor or worn sensor itself (causing rich running), or a loose connection between the TPS and the ECU.

All solutions are in the Wiki.

[NigelA]

Very many thanks,Grrrmachine. Much appreciated.