86 911 miss under acceleration

Paul T · 02-28-2002, 04:39 AM

I'm having an intermittent problem with my 86 that I'm hoping someone can shed some light on. I have recently developed an intermittent miss at idle (hot or cold though seems better when hot). Every now and then a cylinder will just drop for a second or two than pick back up. Also, I get a pretty bad hesitation under light throttle acceleration, almost feels like fuel starvation, but if I increase the throttle it smoothes out and feels fine. I have recently (within the past 10,000 miles) replaced plugs, cap, rotor, fuel filter and adjusted valves. I had the injectors cleaned a couple of years ago and I have always had a suspicion that these might be clogged. Prior to this the car has ran great although it has never had as smooth an idle as I thought it should. I also tourqued the intake and checked hoses and didn't find any obvious leaks. Any ideas ? I unfortunately don't have a ton of time and don't have the $ to just start replacing parts. Am planning on spending Sat with the bently manual and a Fluke tester but just thought I'd see if anyone has had similar issues. Thanks for the help!!

Rick Lee · Rick Lee's Garage

If all else fails, replacing the DME relay seems to be a very popular cure-all on this board. I chipped my P-car and it runs a little smoother than before, though it never had the symptoms you describe.

dickster · 02-28-2002, 05:56 AM

yours sounds similar to mine - i was convinced i had intake leaks.

one of ky symptoms is that it will stall when i reverse it up my driveway into the garage - unless i give it plenty of revs.

i spoke to amd (uk) and they said its probably nothing. well i had the car dynoed today - and there ain't much wrong with it.

i'm going for a rechip sooner or later, hopefully that will help.

Paul T · 02-28-2002, 07:29 AM

Rich, thanks for the advice...I forgot to mention that I changed the DME relay just a week ago in hopes that would be an easy cure but no such luck. At least now I have a spare which I should have been carrying anyway, I guess....

Kurt B · 02-28-2002, 07:30 AM

I had a similar problem a few years ago suspected to be intake leaks turned out to be 3 bad injectors. Misses at idle--stumbling, but when you punch it, it smoothes out. I wound up replacing all of the injectors.

Paul T · 02-28-2002, 07:32 AM

Kurt, I'm thinking of going that route also....just wish they were not so expensive!

stlrj · 02-28-2002, 09:35 AM

I had a plug fail in less than 10K, so I no longer assume that it can't be that.

Besides, you might be kicking yourself when you find out that's all it was after throwing a lot of money away on fancy fixes that didn't work.

Joe

nhromyak · nhromyak's Garage

Check your head temp sensor... is it the one wire type?

Check grounds on intake Cylinder #1.

Replace DME relay... you have a spare? Right?

Re-torque intake seals, check all rubber boots on intake.

Good Luck.

Kurt B · 02-28-2002, 11:28 AM

My experience is, even a bad intake sealing doesn't make it miss like bad injectors. Intake leaks may drain power, but they don't cause the missing since I screwed around with the intake leaks for a few weeks before I gave up--going with both good and bad sealing, and it never changed for the worse.

Peter Kelly · 02-28-2002, 04:09 PM

When you get your fluke meter out, the first thing I would test is the resistance and action of the air flow meter. this is the barn door device that measures the air flow in. It is a simple potentiometer (electrically). Both the bently and haynes manuals describe how to test it.

I'll bet yours is bad. Very common problem as these cars get older.

-Peter

Dignan · 10-02-2002, 03:57 PM

Hey,
I have a 78SC with SSI's and a GHL duel in duel out. but i have somewhat the opposite that you all describe?

I have a great idle after warm up and have the hesitation or missing under acceration.. any I deas.. I have replaced the accumulator, fuel pump, will this week end replace the filter and I would think the plugs are fine.. at night i can see NO archs or anything....

any help would be great

Eric

LeRoux Strydom · 10-02-2002, 10:55 PM

You might want to check all the spark plug connectors and plug wire connectors at the distributor side with a digital multimeter. I can't remember the details, but these have a resistance spec described in the Bentley manual. I once had a misfire under light acceleration that turned out to be a bad plug wire connector at the distributor.

Good luck

LeRoux

Dignan · 10-03-2002, 02:47 AM

Thanks Lroux,
I'll sort through that this weekend .. I hope that is it..

eric

jabb · 10-03-2002, 04:19 AM

Something tha is easy to check is disconnect the O2 sensor and see if it runs any better