Author Topic: Idle bouncing all over (Read 4409 times)

mermco · « **on:** May 27, 2012, 02:17:34 PM »

Sorry if this is whipping a dead horse but I have been unable to find my problem or a solution anywhere on this or other sites so here goes. Just recently replaced the head on my 1992 318ic. Car runs well at highway speeds and gets good mileage. But it won't idle for crap. Will do fairly well for a little bit but will shudder and start bouncing between 450 - 1000 rpms. Acts like it is going to die on the low rpms and then shudders and bounces back up. I have replaced all the vacuum hoses under the intake. Changed the intake boot, replaced the ICV, swapped MAF, tried 3 different cam sensors, replaced the coolant temp sensor, changed coils and wires, fuel filter replaced two months ago and the fuel pump is about 18 months old, swapped o2 sensors with an old one I had here from a good running car. I cannot get this figured out. Could my DME be causing this? I have to say that I am ok with mechanical repairs but the magic of electricity is out of my comfort area. I have tried just about all that I can think of and need the help on those more experienced and knoledgeable than I am. Thanks in advance for your help.

mermco · « **Reply #1 on:** May 27, 2012, 02:27:25 PM »

Forgot to add that there are no cel's and stomp test shows 1444.

thedguy · « **Reply #2 on:** June 03, 2012, 04:24:02 PM »

If the issue happened when you replaced the head, I'd double check the cam gears are tight, since the factory ones have about 3 degrees of adjustment (IIRC) they could be shifting around at low engine speeds.

mermco · « **Reply #3 on:** June 06, 2012, 03:20:25 PM »

Thanks, I'll check that out. I have also swapped the DME, the relays under the cover on the firewall, the TPS and the oil filler cap. Pulled the intake manifolds and cleaned them again along with the throttle body. Non of these things have made any difference. Pullin' my hair out on this.

DesktopDave · « **Reply #4 on:** June 06, 2012, 03:36:11 PM »

You've replaced every item that could cause this, as far as I can see. Personally, I'd be curious about the DME output to the ICV. Not sure how to do that while it's running, maybe an inline test LED wired into the cabin. How well does it idle with the ICV unplugged?

I have also had one bad brand-new ICV right out of the box.

You think you're not that good with electrics, but a cheap digital multi-meter can eliminate a lot of frustration with a few simple tests. I'd urge you to try one out.

mermco · « **Reply #5 on:** June 06, 2012, 04:13:41 PM »

One more odd thing. When I turn on the ac the idle smooths out quite a bit. Still isn't prefect but is definitely better.

mermco · « **Reply #6 on:** June 06, 2012, 07:43:10 PM »

I am on my second DME and it runs the same. Just noticed that the bad idle gets better when I take the oil filler cap off. Anybody have an opinion about possible issue with crank sensor or alternator maybe? My inclination is that the crank and cam sensors are working since the car starts up fine and runs well at highway speeds. Something that seems to happen is that it seems to idle fairly well at start up but starts to run bad when it starts to get warmed up. Could my O2 sensor be causing all of this headache? Thanks for all of the input past, present and future.

thedguy · « **Reply #7 on:** June 07, 2012, 03:09:45 AM »

I don't see how, but maybe it's a PCV problem? Only thing I could think that would make it better when the cap went off.

I'm starting to wonder if you have a general wiring issue, poor ground or issue with signal from a sensor to the ecu.

Have you been having any issues with the battery going dead? Have you verified the alternator output? This sounds VAGUELY similar to when my alternator was going out. High revs it would generally work but at idle it wouldn't. I replaced the brushes /regulator on the back from a volvo (I just pulled out the one from my cars alternator and found 4 or 5 that looked similar, the best one worked great so far).

Did you ever verify the timing on the cams? And has this been going on ever since the head was replaced or did this come around a while later?

mermco · « **Reply #8 on:** June 07, 2012, 09:58:54 AM »

This car belongs to my daughter who lives a couple hundred miles away. She has said that she doesn't remember just exactly what it was doing before she brought it to me but i seem to recall that is was running poorly which is what prompted me to cange the fuel filter early on and then i almost immediately noticed that she had a head issue. So it probably had this problem to some degree before it came to me.

I have cleaned the battery ground but have not looked at the ground from the block to the chassis. I will do that this morning. Can't believe I haven't done that already. I am thinking that a cam timing issue would present itself through the whole driving range not just at idle. I plan to pull the alternator and take it to be checked out today if time permits. I am of the impression that an e30 m42 does not have a pcv that could go bad.

Does anyone know if the fuel tank breather valve or the carbon canister could cause any issues like this? Again, I am not getting a cel and stomp test just shows 1444.

Please Lord, don't let it be an electrical issue!

mermco · « **Reply #9 on:** June 07, 2012, 04:25:40 PM »

Update: Cleaned my grounds (all that I could find anyway) and no change to dropping and surging idle. I will have my alternator tested but I an not having any other issues with the charging system. I guess i will have to bite the bullet and take it to the shop.

mermco · « **Reply #10 on:** June 11, 2012, 01:59:05 PM »

After talking with my daughter the cars owner i found out that this issue was happening before the head rebuild. So this week-end I replaced the o2 with a new bosch unit and still no significant change. Does anyone know if a faulty fuel pressure valve could be causing all of this?

mermco · « **Reply #11 on:** June 28, 2012, 10:53:00 AM »

Took the car to the shop. They said they found vacuum leaks and fixed them to the tune of $365. Told me the idle was still a bit "rough" but all it needed was to be driven for a few cycles. Damn thing runs worse now than when I took it to them. Returned the car to mechanics and now they are "thinking" maybe it's an injector problem. Since all of the plugs look the same (a nice light ash color) I don't see how this could be the issue. Anybody got any ideas?

mermco · « **Reply #12 on:** July 03, 2012, 06:29:48 PM »

Got the car back from the shop. They gave up. Injectors were good. All they could find was a high carbon reading when the idle was acting up and cylinder compression was running kind of high. They are stumped, I am stumped. Life goes on.

romeomike · « **Reply #13 on:** July 23, 2012, 10:42:33 PM »

I'll second thedguy's advice to check your alternator brushes and replace if necessary.

After that, for a short season consider undoing the electrical connector to the ICV and see if that calms things down. It will light your CEL, but for the moment I don't have the surge blips (mine were from 1300 to 1600) or idle speeds anywhere from stalling to around 1100.

For reference in the last year or two, I've done virtually all the vacuum/coolant/fuel hoses, oxygen sensor, degunked both intake manifolds, new injector o-rings, ECU coolant temp sensor, and fuel filter. I'll be swapping ICVs this weekend to go with installing a quieter aux fan.

Update: Cleaned ICV installed. Don't have the wild blips, but low idle a bit problematic in spots. Undid negative battery cable to clear DME codes. We'll see how it goes with a fresh start.

Update: car didn't start, but God granted me three breaks: I was in my garage, quickly traced it to a failed main relay, and had the spare part in the trunk. We're in good running shape now.