325is, high idle only when warm

[Sonic]

I have a problem with the idle on my e30, that all the usual solutions don't fix.

Car: 88 325is, 167k. Engine mods: Turner chip, IE SS exhaust.

Problem: High, steady idle. Engine idles steadily at 1500rpm with no surge.

Other symptoms: Poor fuel economy, runs rich (black puff out of tailpipe when throttle pressed), when dip stick is removed, idle goes LOWER. When Coolant temp sensor wire is disconnected, idle is perfect. When O2 sensor is disconnected, no change.

Parts recently replaced (in last 1k): Injectors (freshly cleaned stock Bosch 715s with 3 bar FPR), throttle body gasket, intake manifold gaskets, valve cover gasket, oil return tube o-rings, oil cap, oil pan gasket, spark plugs, coolant temp sensor, throttle switch,

Replaced in last year: Air intake boot, throttle body to valve cover hose, ICV to throttle body hose, cap, rotor.

Other parts checked: ICV is in perfect operating condition, and has been replaced sometime in the cars life. Valves adjusted, AFM door moves freely, O2 sensor has 30k on it and was OEM, plug wires

Originally I replaced the throttle switch as it was not sending a proper idle signal, and it does now. When the car is warm, idle is high at 1500, and the car runs rich and gets horrible gas mileage. I also had higher flow injectors in the car.

After I replaced all of the intake gaskets thinking it was a vac leak, with no results. I see no place where a vacuum leak coudl happen, and have sprayed FI cleaner everythere I thought there might be a problem, with no results. Then I replaced the high flow injectors with perfectly operating stock injectors: no change. Replaced Turner chip with stock: no change.

Performance is great...car has all the power it should and drives well, except for an slight stutter when giving it gas from idle to get going.

I don't know what could possibly be the problem. I have replaced/checked everything that has to do with the idle on the car with no results. This is frusterating. Any ideas?

[jase007]

Sonic:

Then I replaced the high flow injectors with perfectly operating stock injectors: no change. Replaced Turner chip with stock: no change.

It looks like you hit most of the tests Bentley mentions.

Have you checked the two "elbows" that go into the throttle body? Here is an article I wrote and posted in this forum.

Sealing Vacuum leaks on M20B25 1990 325iX

Since then, I pulled the IM and head and had the head rebuilt. In the process of doing another detailed writeup. All back together and sounding great. At 219,213 miles ... all of the rockers were pitted and worn out, the camshaft was worn out and the valve guides were shot. Valves were good, head was straight, car never broke a belt or overheated. I bought it in 1993 with ~23,xxx miles on it. I would hazard a guess that your cylinder head might nead the same work.

Have you covered all of these seals / bellows already:

1. valve cover
2. rubber cam plugs in ends of head
3. valve cover to t-body breather hose
4. T-body to IM gasket
5. Intake bellow - AFM to IM
6. breather pipe and o-rings from block to IM
7. IM gaskets
8. oil cap seal
9. oil dipstick O ring
10. connecting tube / hose at bottom of oil dipstick housing with two hose clamps on it to hold to the block inlet
11. ICV to T-body hose [put a zip tie on this to tighten]
12. vacuum hose under the T-body to charcoal emissions purge tank.


Typically, a rich running motor will "gallop" or "lope" at a low idle... and stall. Pull a vacuum [mitty-vac tool] on your FPR and make sure the internal diaphram isn't busted. Put the OEM FPR back on there in good working condition while you are troubleshooting [I would do this will all the OEM pieces and then change out one at a time].

On our cars ... the unmetered air downstream of the AFM causes a lean running motor .. the ECU [O2 sensor] sees this and richens it up ... viscious cycle... However, you have a high idle AND are running rich. I think [99% sure] your injectors and adjustable FPR aren't set up correctly for correct fuel pressure at idle or throttle tip in. Did you put the mustang injectors in there? Take the OEM Bosch injectors and get them serviced [$20 a piece] and reinstall with OEM FPR and see what you have.

When you swapped all of the injectors back in ... did you pull the neg. batery cable and let the ECU reset? Same Q for all of the other replace stock parts and retry?

Who made the adjustable FPR?

Where is the stop set for the t-body to rest? Have you adjusted it? [set by the factory]. Did you change the internals on the AFM?[use the bigger AFM with the M20B25 internals]

Where is your throttle cable adjusted to? Does it have the .7 - 1.?mm free play that Bentley's tells you? Same Q for cruise control cable...

Let us know ....

Jase

[Sonic]

Jase,
Thanks for the reply.

Originally posted by jase007
[Have you checked the two "elbows" that go into the throttle body? Here is an article I wrote and posted in this forum.

Yes, I have...they were loose so I sealed them with some hi-temp RTV. I may epoxy them in though, I see no need for them to be able to swivel.

Since then, I pulled the IM and head and had the head rebuilt. In the process of doing another detailed writeup. All back together and sounding great. At 219,213 miles ... all of the rockers were pitted and worn out, the camshaft was worn out and the valve guides were shot. Valves were good, head was straight, car never broke a belt or overheated. I bought it in 1993 with ~23,xxx miles on it. I would hazard a guess that your cylinder head might nead the same work.

The head on this car has been replaced at some point. When I got the car at 123k it looked brand new, and even today there is not even any discoloring inside the head, and no sign of wear on any of the componants, or even any carbon on the intake valves.

Have you covered all of these seals / bellows already:

1. valve cover - replaced
2. rubber cam plugs in ends of head - no signs of oil leaks, see above for head condition
3. valve cover to t-body breather hose - replaced recently
4. T-body to IM gasket - just replaced
5. Intake bellow - AFM to IM - recently replaced
6. breather pipe and o-rings from block to IM - just replaced
7. IM gaskets - just replaced
8. oil cap seal - just replaced
9. oil dipstick O ring - seals well, good condition
10. connecting tube / hose at bottom of oil dipstick housing with two hose clamps on it to hold to the block inlet - oil dipstick tube seals well - when dipstick is removed, idle drops noticeably.
11. ICV to T-body hose [put a zip tie on this to tighten] - replaced recently
12. vacuum hose under the T-body to charcoal emissions purge tank - good condition - have plugged it and the port in the TB with no change.

All of the parts came from Pelican, too :-)

Typically, a rich running motor will "gallop" or "lope" at a low idle... and stall. Pull a vacuum [mitty-vac tool] on your FPR and make sure the internal diaphram isn't busted. Put the OEM FPR back on there in good working condition while you are troubleshooting [I would do this will all the OEM pieces and then change out one at a time].

I'm using the OEM 3 bar FPR with the stock injectors now. There is no gallop at idle.

On our cars ... the unmetered air downstream of the AFM causes a lean running motor .. the ECU [O2 sensor] sees this and richens it up ... viscious cycle... However, you have a high idle AND are running rich. I think [99% sure] your injectors and adjustable FPR aren't set up correctly for correct fuel pressure at idle or throttle tip in. Did you put the mustang injectors in there? Take the OEM Bosch injectors and get them serviced [$20 a piece] and reinstall with OEM FPR and see what you have.

I had M30 injectors in there (freshly serviced) with an eta 2.5 bar FPR, giving a flow rate of about 175cc, compared to the stock 153cc.

When you swapped all of the injectors back in ... did you pull the neg. batery cable and let the ECU reset? Same Q for all of the other replace stock parts and retry?

Yes...always reset the ECU.

Who made the adjustable FPR?

There never was an adjustable FPR, I used 2 different BMW FPRs, an "i" 3 bar and an eta 2.5 bar, depending on the size of the injectors.

Where is the stop set for the t-body to rest? Have you adjusted it? [set by the factory]. Did you change the internals on the AFM?[use the bigger AFM with the M20B25 internals]

TB stop is set per factory specs. Changing it does not lower the idle at all. It has not been touched since the time when the car would idle properly. AFM is a stock M20 unit, but the cap covering the adjusting screw near the outlet has been removed, so it may have been adjusted. The car had an eta intake manifold and TB on it with mismatched injectors when I bought it. I changed to the i intake pieces a long time ago, and have had it work properly.

Where is your throttle cable adjusted to? Does it have the .7 - 1.?mm free play that Bentley's tells you? Same Q for cruise control cable...

Plenty of slack. Perhaps too much.

I'm going to check the wiring from the Coolant temp sensor to the DME to see if it has continuity and isn't shorting. I may also try another DME, just to rule it out.

Thanks for your help so far!

Chris

[jase007]

Chris:

AFM is a stock M20 unit, but the cap covering the adjusting screw near the outlet has been removed, so it may have been adjusted.

Can you borrow another AFM to try? [make sure spring wasn't tightened]. If the cover has been removed .... take a look at yours and see if there are wear tracks where the needle tracks over the arch contact [basically a big potentiometer like the throttle position switch].

Here is an excellent AFM site from a Porsche 944 guru that I have used for diagnostics. Same / similar AFM.

FRWilk's Site - 944 AFm subpage

It is also a good time to test the intake air temp sensor in the AFM.

From Bill Taylor's BMW site:

"and,,,i add to the other two, who shared how to's on repair of the afm.... the temp sensor....

it is located at the intake side of the afm,
looks like a neon indicater...when this thing goes, your engine is
either extreemly rich or lean,

i went and bought a used afm , bosche, for $40.00, removed the temp
sensor, via the black top where the wiper arm resides, r& r temp sensor
and was back on the road....

you can check your temp sensor by spraying the unit with compressed
air,or butane, from a canister to make cold and heat from a propane
torch , held close but not too close...

and reading with a VTM...you should see a swing in resistance, as the
temp varies...no variation...bad temp sensor...replace, varying
resistance,ok.....look some other place

richard, euro wrench"

If nothing is "mechanically" increasing the idle speed ... then it has to be a signal coming from one of the many sensors. If the two temp sensors on the t-stat housing check out .... then I'd head back into the AFM with some of these tests or back into the throttle position sensor on the t-body.

Just some thoughts.

Jase

[Sonic]

Jase,
Thanks for the suggestions.

I have a used AFM and 173 DME on their way to me to test, as that seems like the only thing left to be failing.

I'll post an update with my findings.

Thanks

[Sonic]

Update - new (used) AFM and DME solved the problem.

Then, a week later the car will not stay running when cold.

It starts up fine, then stalls. As soon as you give it gas, stall. As it warms up, it will let you give it more gas before stalling, until it warms up and it is fine.

Oh well, there's always something on an 18 year old car.

[MBEngineering]

HI when you did the valve clearances did the prob' start from then/get worse, if so the engine is pulling in air from the stem seals, so re'adjust the valves slacker and try that, good luck

regards mike

[Sonic]

Hi, Thanks for the reply.

It was the used AFM that I got to fix the high idle. When I removed it and put the previous one back in, the starting problem was fixed, but the high idle was back. I now have another used but known good from a trusted source AFM on the way.

[jase007]

Chris:

Any luck with the 2nd used AFM to solve the high idle or cold stall?

Jason

[Sonic]

A little...

The cold stall is gone, but the high idle returned, but it is not as bad. It will still idle high, but once you STOP and sit for a few seconds, it comes down. With the A/C on, the idle is up at about 2k RPM until you stop, where it gradually comes back down to 900. If you are driving and step on the clutch, it will stay high...it won't go down until you are at a complete stop.

I've tried resetting the ECU and gone over all the vac connections again. Not sure what to do at this point.