325i rough idle, hesitation

[ewolfe57]

I'm working on troubleshooting my sister's '88 325i and would love a little help diagnosing the issue. The main problem is a rough idle with some hesitation and stuttering on throttle. It seems to be running super lean based on what we've determined.
The plugs plugs she had in it for a few thousand miles I think (NGK zgr5a) were straight up WHITE on the ground strap and insulator; new plugs made it run better but after four days they're already pretty white (not as bad as before but still).
We tested the fuel system, pump is running and FPR is working fine. Fuel pressure while engine was running was about 38 or 39 PSI.
Didn't test the injectors yet.
New plugs/wires.
Pressure test came up pretty low...cylinder 4 and 2 were in the mid 90s, the rest were about 120. Oil in the cylinders didn't raise pressure.
There's no smoke in the exhaust or coolant on the dipstick; gonna change the oil soon and check to see what it looks like.
The plan is to adjust the valves and see what happens plus the oil change.
Any ideas what this could be? Headgasket seems possible but I'd expect some of the other normal signs besides low pressure. I'll try to get some pictures of the plugs up if that would help.

[mazzo]

Any smoke test and stomp test (in case of CEL)?

[m3x1c0]

Sisters BF here. These are the plugs we pulled. Could burning coolant result in a plug like this? Car seems to be running fine with new plugs for the moment.

[pandaboo911]

325i rough idle, hesitation

Did you test fuel pressure under load? Pressure doesn't indicate flow. A clogged filter will still allow good fuel pressure but as soon as there's any fuel demand the pressure will drop off.

Do a valve adjustment and check all vacuum lines and ports for cracks. Check oil vapor line for cracks. Any vacuum related rubber parts that are hardened, and not soft like rubber should be, probably need replacing.

That doesn't mean throw parts at it, but start with the cheap more, more common failures first :)


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[m3x1c0]

Did you test fuel pressure under load? Pressure doesn't indicate flow. A clogged filter will still allow good fuel pressure but as soon as there's any fuel demand the pressure will drop off.

Do a valve adjustment and check all vacuum lines and ports for cracks. Check oil vapor line for cracks. Any vacuum related rubber parts that are hardened, and not soft like rubber should be, probably need replacing.

That doesn't mean throw parts at it, but start with the cheap more, more common failures first :)


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No not under load. We did try the fuel delivery tests recommended in the Bentley manual. Jumping the relay contacts did not seem to work. The manual does not adequately describe the test but I believe we did it correctly. I just so happen to have a new fuel filter and will throw that on tonight. The plugs are very white however. If it was a fuel starvation issue I'd expect the fuel pressure even in park to be very low.

[dnguyen1963]

A good general reference on how to read the color of the spark plugs.

https://www.youtube.com/watch?v=saCDmyiBmb0

Your engine is running extremely lean. I would watch out for overheating if I were you. You could also potentially leak coolant into the cylinder resulting to the white calcium deposit on the plugs. Since you had very low pressure on some of the cylinders, I suspect that you will need to look at the HG for leakage.

[m3x1c0]

A good general reference on how to read the color of the spark plugs.

https://www.youtube.com/watch?v=saCDmyiBmb0

Your engine is running extremely lean. I would watch out for overheating if I were you. You could also potentially leak coolant into the cylinder resulting to the white calcium deposit on the plugs. Since you had very low pressure on some of the cylinders, I suspect that you will need to look at the HG for leakage.

That is our suspicion as well. Usually would test this definitively with a combustion leak detector (one of these badboys:https://www.amazon.com/Lisle-75500-C.../dp/B0007ZDRUI) However, I don't think that test would be accurate without being jammed directly in the radiator which is not possible on this car.

The trouble is determining if the white on the plugs is from a lean condition or coolant. So far nothing I've seen points to a fuel issue. Other than the o2 sensor (testing that is on the list) is there anything else that could cause a lean condition?

[15Michaeljoseph]

My money is on extreme vac leak/ intate manifold gasket. While the car is idling, spray starting fluid or brake cleaner around the intake manifold mounting points, and throttle body vac lines. See if the idle changes. Thats how i found my intake manifold gasket to be bad, and my symptoms were very similar to yours.

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[pandaboo911]

325i rough idle, hesitation

+1
With a Head gasket failure you'd have pressurized coolant, oil in your coolant, coolant in your oil, overheating, etc.

If you doubt the condition of any hoses just replace em. They are cheap.
Clean out your icv with carb cleaner or leave the valve side in gasoline/diesel over night.

Check your AFM flap to see if it's moving freely. Try not spray any hardcore solvent on the IAT sensor, only use MAF cleaner for that.



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[m3x1c0]

Thanks everyone for the suggestions. We just checked a valve adjustment to .010 and checked the oil. So far the car runs decent with a little bit of rough idle and the oil did not show signs of coolant. While adjusting the valve I couldn't help but notice how clean the head is internally. There is no carbon buildup whatsoever. The engine was supposedly replaced last year and clearly has been taken care of since then.

I am planning on rebuilding the injectors and changing the fuel filter to see if that clears up the lean condition and smooths out the idle. I've also been told to set the valves to .011 when its properly cold. We shall see.

I'm still highly suspicious of the compression numbers. I suppose if the headgasket is failing it has not done so completely. For the meantime we will correct the lean condition and see if the headgasket situation clears up or worsens. The price of a leakdown is about as much as the parts required to replace the headgasket. So if it worsens I hope it will make itself obvious over time.

Thanks again for the help folks. If anyone in Central VA or NC has a leakdown tester and would be willing to perform the test for a reasonable price please contact me.

[RobDog]

I had a rough idle and the car would act like it wanted to stall. It turned out to be a vac leak at the metal elbow that connect the throttle body to the brake booster and also the ICV elbow. These metal press fitting come loose over time and gave my hell. The engine has the most vacuum at idle so when looking at them they looked good because the vacuum kept them in place. The second I would start driving they would slip out. I did not catch it until one came all the way out and My Idle and braking went to shit. I JB welding them into place and have been good ever since.