87 Carrera Stumbling

[tx63conv]

New to me 87 Carrera—changed the oil last weekend and went for a short drive. Didn’t get 100 yards and the car started stumbling. Will idle fine at about 900 rpm but I ease into the gas and at ~1200 it stumbles. Off the gas, right back to idle. After a few times, I was able to limp it back. Checked the oil—low (10 qts in) but didn’t really get it up to temp. Started the car, let it idle for a few minutes and was able to drive it around the neighborhood and up to temp. Was low on oil so I parked then got sidetracked.

Yesterday (sat for 7 days), another quart in (11 total less spillage) and same problem, was able to get down the street and shift in to second then nearly stalled. Idles fine, but stumbles at about 1200. After idling for a few minutes, was able to limp it back by keeping RPMs above 1600. Checked oil, ˝ qt low and topped off (11.5 qts in).

After idling for several minutes while checking oil and fiddling around trying to figure out the issue, I tried a test drive again and no issues. I assume the oil change and the stumbling are a coincidence. I did spill some due to the funnel I had and it got around the spark plug—I don’t think the fuel rail. I also had a no start issue late August that was due to the ref sensor being bad. Replaced both the ref and the speed sensor in September and no issues. Went on a long 100+ mile drive 3 weeks ago.

I assume this is an electronic issue but not sure where to start. Thoughts?

I am posting a separate email about the oil change—as it was my first time.

[tx63conv]

Any thoughts on this. Car is at my shop and and exhibits the same attributes. Will idle fine at 900 then stumbles to 1200. Eventually after warming up, I can rev a few times past 1200 (still stumbles). Then seems to go away.

Any ideas of where to start? Vacuum? I had Ingo look at the DME when I had a no start issue and he said it was fine.

[Tea Tray]

First thing is to check for vacuum leaks. There’s no shortage of vacuum lines, clamps and strange connections back near the firewall over and heading to the oil tank. Also the large vac line on the very left side of the firewall - that heads up front to the brake booster.
Also check the injector electrical connector that sits about in the middle of the firewall. Mine was blue with corrosion.
No fun to get at back there.
Lastly and most importantly, check your fuel lines and carry a fire extinguisher.

[tx63conv]

Thanks! I would think that a vac line issue would be present and cause the car not to run well at all. My problem goes away after warming up. My thought is fuel delivery off idle due to a sensor. I did have an oil spill around the #4 plug and used some shop towels to clean that up. I will investigate around there.

[dtxscott]

Originally Posted by tx63conv

Thanks! I would think that a vac line issue would be present and cause the car not to run well at all. My problem goes away after warming up. My thought is fuel delivery off idle due to a sensor. I did have an oil spill around the #4 plug and used some shop towels to clean that up. I will investigate around there.

Were you able to resolve the issue? I have something similar where it stumbles/vibrates at 1600 then goes away when warm.

I will investigate mixture settings on the barn door as I think the mixture is lean.

[wjdunham]

Of course there are many things that can cause this sort of intermittent issue, but the first culprit I would check is the Cylinder Head Temp sensor. If the car is new to you and you don't know the full history, it would be a good idea to replace the CHT sensor, and the Speed and Reference sensors since they are all in the same area and you will already have enough of the heater stuff cleared out of the way to run the wiring through the engine tin. If the speed or reference sensor goes bad you will be getting a ride home on a flatbed so good to have them in a known state. Bad CHT can cause starting issues, or intermittent/stumbling due to fuel mixture being all wrong and the effect of the improper mixture can change as the engine warms up.

Bill

[stlrj]

"I assume this is an electronic issue but not sure where to start. Thoughts?"

Has all the earmarks of an ignition problem and best to start is at the weakest point which would be the problematic Beru ignition cables

If you spray some windex on the cables while at idle you might get your answer.