Car is an '84 245ti. I'm experiencing very high idle when in Park (~2500) which drops to ~1500 when in Drive. Over the past few years I think I've replaced all the engine sensors except the Thermo Time Switch. Do you think this could be causing the problem? Any other ideas about what might be going on?

Thanks,
Corey
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1966 122s + 1984 245ti + 2000 v70glt = much to learn!

Hello,

Having an 82 K-Jet with CIS I have had some experience with idle speed. If you have changed all the sensors and the CIS ECU/ICV I would look at the following:

Have you done the base idle set up. If it is out of whack the CIS cannot bring the idle in range.

Is there voltage(12v) between pin 1(+) & pin 2(-) of the ECU. The voltage on my 82 goes through the seat belt reminder unit to fuse 13. No voltage= no idle control.

Have you checked the throttle switch for function. Pin 2 of switch should loose it ground on idle, this signals the CIS to take over idle control (pin 8 CIS ECU)

The temperature control sensor when hot should have a very low resistance across the leads (approx. 200 ohms). This low resistance should also be across pins 9&11 of the CIS/ECU. You might have an open or corroded wire from the sensor to the ECU. The higher the resistance or open = high idle.

Hope this helps.

Mario









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82 242 DL-MPG

Update to my original post...

After switching out the CIS computer (no change) and the Idle Air valve (no change) and checking for vacuum leaks (none found) and checking the throttle switch (ok) and confirming no binding of the accelerator cable I tried the following:

Disconnected the CIS computer = no change to high idle problem.

Then I used vice grips to pinch inlet hose of Idle Air valve and that casued the rpms to drop significantly. So I blocked the Idle Air inlet hose and set the base idle to ~1000rpm.

So I now have the CIS computer disconnected and the Idle Air valve blocked and the car idles and seems to be running perfectly.

Question: is there any reason I shouldn't run with this set up? Am I going to damage/disrupt any other parts of the system?

Thanks

I had a similar problem that I still haven't figured out. I have an 85 240ti B21 with CIS. Mine at start up even under 50 degrees no fast idle and some times stalls. But after warm up and drive when I stop put in park or nutral idle is 1100 to 1200 RPM's. But shut it off and restart my idle is at 900 RPM's I have gone through the hole system. Fuel pressure tests in range,All electrical tests show O.K., Replaced Idle control valve,ECU,All wires through firewall O>K>,Checked injecters O.K. Rebuilt FPR,coolent temp. sensor new,Throttle switch adjusted,cleaned throttle body,checked and replaced most vac. lines,replaced intake manifold gasket,set dwell,timing and base idle.
The only way I could get the engine to idle wright was after the drive put in park and use the idle screw to lower idle to 900RPM's (then that changes the Base Idle) and stops that from happening again. It solves the problem for now but not the cause of the problem.I have had this problem for over a year and don't have any idea. Now I have something new happening,At start up idles fine for 30 sec. then starts to hunt from 900RPM's to 800RPM's for about 30 sec.then stearts to smooth out.I'm just living with that for now.If you find an answer to you problem please post and I will do the same. Good Luck,Charlie

My guess now is that I've got a wiring issue between the CIS computer and the air idle valve causing the valve to stay open all the time. I tried two different computers and two different idle valves and saw no change to the high idle problem. I'm going to try to run the car with the idle valve plugged and see what happens. So far it seems to be fine but it's only been a couple days...
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1966 122s + 1984 245ti + 2000 v70glt = much to learn!

The signal to the valve is a square wave. the center pin is 12volts and the outer 2 pins are out of phase. You may get some insight with a voltmeter, but an O scope will tell the whole story.
The control boxes do fail, so it is possible to have 2 bad ones. May want to try them on another car before saying they are OK.
I have run CIS cars without the control boxes, and mostly this is fine. But when cold or running AC the idle may not be high enough to keep it running.
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84 242Ti IPD bars&springs, 89 745 16v M46 IPD bars, 89 744 16v M46 IPD bars, 93 945 Turbo AW71, 91 245SE AW70 IPD bars, 93 245 CLassic M47

Even tho we have similar problems this may lead to a wiring issue. I also tried 2 ECU's and 2 ACV's and no change.
Plugging the idle valve like you did works but doesn't solve your problem. It's like me when I have the high idle I back out the throttle adj. screw so it will idle at 900 rpm's but then I have changed the base idle.This is so frustrating not being able to solve this problem so, I let it alone for a while and then with a clear head(if that's possible)dive in again. Charlie

Some more information that may or may not be useful:

This car hadn't been driven for a couple months. I started it and allowed it to idle to charge the battery. Idle was fine for about 5 minutes then the engine died. It's when I restarted the car that the rpms jumped to ~2500.

Any other ideas about this problem are appreciated!
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1966 122s + 1984 245ti + 2000 v70glt = much to learn!

My experience with several 240T's wiht this problem is the idle computer. Located in the passenger footwell, its the smaller, black plastic box. I've seen several of these go bad...

Switched out the idle computer but no change...
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1966 122s + 1984 245ti + 2000 v70glt = much to learn!

Thanks for the suggestion. I think I've got a spare computer so I'll pop that in and see if that affects the idle.

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1966 122s + 1984 245ti + 2000 v70glt = much to learn!

Have you ruled out badly leaking injector seals? With the engine idling, spray or mist each injector with water and see if the idle drops after spraying any or all of them. If you haven't already done so, you could also remove the throttle body and clean it thoroughly with a can of fuel injection cleaner.

Haven't done the spray test on the injectors but they've all been replaced within the last year or so. If the computer swap doesn't take care of the issue I'll pull the throttle body and have a look at that.

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1966 122s + 1984 245ti + 2000 v70glt = much to learn!

Check all throttle linkages and throttle cable as per Haynes or Bentley to make sure that the throttle is closed at idle. Also check that the kickdown cable is not preventing the throttle from closing - kickdown cable should have a couple of mm of slack at idle. Then check stuff that allows "idle air" to bypass the throttle. For example auxiliary air valve & its electrical connections, idle speed screw position and O-ring, etc (if your car has this stuff or its equivalent such as CIS "idle motor" etc) and all rubber hoses etc. I removed all rubber hoses for inspection - there can be subtle cracking.

Excess idle RPM is generally due to excess throttle or its equivalent being excess metered air (which bypasses the throttle) for fuel injected vehicles.
I've found that excess unmetered air (particularly due to leaking fuel injector seals) makes the car difficult or impossible to start as it leans the mixture. Never found it to significantly increase idle speed.

Apparently ignition timing can significantly affect idle speed (put a large syringe on the distributor vacuum advance line (if you have one) and pull and push the syringe plunger demonstrates this). Defective vacuum delay valve in the distributor vacuum line can cause trouble - I put mine in the rubbish - its an anti-pollution feature - only fitted on some cars. Also some ECUs can use timing to adjust idle speed (used only during engine warmup?)

I'm really interested in your problem as I had fast idle of 2500 RPM after driving on "washboard" roads for a couple of hours. The problem then persisted for about one week on smooth bitumen roads then went away. No one on BrickBoard answered this hassle (with 1979 K-Jetronic - transistorised ignition only - no ECU). (I chopped up an auxilliary air valve out of curiosity but it is such a simple device I don't see how it could get stuck open - anyway its supposed to increase idle at warm up by only a few hundred RPM (speed in Neutral)). Likewise the aircon "idle-up" valve can only increase idle by a couple of hundred RPM (speed in Neutral). Don't see how they can give 2500RPM.

My wife's 1987 car had fast 2500 RPM idle but this was on a carburettor vehicle in which fuel gum around the carby caused the fast idle cam to often stick. Quick spray with carby cleaner fixed that one - no need to dismantle.

Hope for a solution before your torque converter burns out or you hit the car in front at the lights!