1988 Porsche 911--rev and hesitation problems

TazerD · 08-14-2002, 12:32 PM

Hello,

I started noticing a hesitation problem with my '88 911 Targa about 3 months ago. I'm not sure if it's exactly what you'd call "hesitation"--while driving, the car occasionally seems to back off...it's still moving forward and the engine is still running, but it feels (to a person who doesn't know much about cars) as if it isn't getting any gas. This hesitation usually lasts for a second or so, and then the car drives normally. Usually, this happens 2-3 times within a couple minutes, but it didn't seem to happen regularly or predictably. After I first noticed the problem, it didn't occur again for at least a couple weeks.

At this point, the problem happens every two or three days. It does NOT seem to happen often when I'm on the highway...I've driven 300 miles without a blip.

However, last night, the problem was the worst it has ever been. (My husband had added fuel injection cleaner that day, and I had a full tank of gas--in case that may be relevant.) The car hesitated for probably 5 seconds (I thought I was going to have to pull off the road), and I kept my foot on the accelerator. Before it started running again normally, it sort of hiccuped/chugged a few times...seemed to start and stop going forward a few times, then zoomed forward as it should.

I also noticed that when I was idling at a stop light, the engine revved up to 3000 rpms...it would go back down to 1000, then rev back up. It did this a few times. This has happened a couple times before, but it doesn't ALWAYS happen along with the hesitation problem. However, with as badly as the car was running, it did seem to be related.

Any ideas about what might be going on? I've taken it to 2 mechanics, who've noticed no obvious problems. And of course, I can't get the car to misbehave on command, so I haven't been able to show them what the problems feel like. Their suggestion has been to keep on driving the car until it gets bad enough that they can see it, but I'm worried about getting stuck on the side of the road (particularly at night).

I didn't mean for this to go on for so long, but if you have any ideas about things we can check, or if you have had a similar problem, I'd really appreciate hearing the details!

Thanks!

JWest · 08-14-2002, 12:37 PM

Just a general help for diagnosis:

Watch the tach as it does it - if ignition related you may see a bobble or jump in the tach - if a fuel problem then the tach will remain steady.

88911coupe · 08-14-2002, 01:49 PM

I hate to fall back on an old standby but it's easy and cheap to replace the DME Relay. Order one from Pelican and it's about a 15 minute fix. At least you can eliminate that as a possible cause and then move onto more compicated things. If it's the original then it should be replaced anyway. Next step may be the cyl head temp sensor...still cheap but sort of a PITA to do yourself.
Good Luck and let us know what happens.

TazerD · 08-14-2002, 02:04 PM

Thanks for the suggestions...I'm going to go out and drive it and see what the tach does.

I replaced the DME relay a couple months ago in hopes that my problem would go away--no such luck. Will replace the temp sensor before I take the car to the beach this weekend!

A friend said that the fuel line might be rusting and giving off little chips that clogged the line...he said that you could cut the fuel line and put in some kind of filter that would stop the chips from interfering with the gas. Anyone think this is another step to take?

Also, is it true that a Porsche dealership can't run diagnostics on an 88?

Milu · 03:09 PM

88s are pre diagnostics.
From your symptoms I would guess you are getting unmetred air entering your fuel injection system, think vacuum leaks etc. This is probably the best start point.

Also...

After DME relay as you've already said, cyl head temp sensor is the next usual suspect on 3.2s, if this is ok..........

Try checking under the drivers seat near the ECU for dampness, this could make your DME and/or ECU play up.

Check distributor cap for connections, cracks or moisture.

As a shot in the dark it might also be worth looking at:

having all the sensors checked out as well as ensuring that all connections are properly pushed in

checking your maintenance records, to see when the plugs and leads were last changed. They can cause some running problems if past their best.

Good luck.

Milu · 08-14-2002, 03:57 PM

Also worth looking at your air metering unit, it could be worn out or just gunged up.

Were the mechanics you went to Porsche specialists?

TazerD · 08-14-2002, 05:08 PM

One guy is a top-notch Porsche mechanic--we've used him for another 911 ('83) that we bought last year, plus a 924S that we've had for awhile. The other mechanic specializes in imports, but he did all the work on my mother's 924 (which we now have).

I drove the car this evening, and the tach didn't go down when the car seemed to hesitate. This seems in line with the idea of a leak or problem with the air/fuel mixture, I think.

It seems like it would be pretty easy (well...for my mechanic, not for me!) to check the air injection system, so I'll probably try that next. Is there any kind of mixture you can add to gasoline to potentially ungum the air metering unit? (I'm not sure how it flows through, so that may be a funny question.)

Thanks for all of your ideas. I'll let you know how it works out!

ischmitz · ischmitz's Garage

I always thought the fuel filter would be one of the first thing to change before looking for tougher gremlins. Am I missing something?

Ingo

Milu · 08-15-2002, 12:02 AM

Air metering unit is basically a tube with a flap inside that opens and closes to control airflow. It may not have been the correct procedure but I've used WD40 to free one up.

Ischmitz, I think you're right that it's best to check the simple stuff first.

08-15-2002, 02:08 AM

I have had similar symptoms with my car. Turned out to be a faulty flywheel sensor.

My car wouldn't idle steadily, it hesitated, and if I kept the gas pedal down during hesitation it would caugh. However this always happened when the car was warm, never when cold!?

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by TazerD
A friend said that the fuel line might be rusting and giving off little chips that clogged the line...he said that you could cut the fuel line and put in some kind of filter that would stop the chips from interfering with the gas. Anyone think this is another step to take?

Not a chance. The car already has a big fuel filter already.
-Chris

TazerD · 08-20-2002, 04:56 PM

I took my car into the shop today after some problems this weekend.

I drove to Nag's Head (@175 miles)...had a couple hesitations going up there, but nothing too bad til the car cut out at milepost 4 (I was going to 8). When I tried to start the car, it sounded like it was just about to turn over, but the engine just couldn't catch.

A guy stopped and asked if I needed help, and I asked if he could jump the car--as soon as we attached the cables, I cranked the car (it started immediately), and I was on my way.

I had the alternator checked and the connections checked/cleaned today. Everything looked fine. My husband and I took the car out to drive it tonight, and it cut off at a stoplight. We pushed it into a parking space, waited a minute, and it started up just fine (but with a plume of blue smoke).

Seems like it might be flooding...I have had the battery checked, too, and it's okay. I'm going to take it back in (hopefully this week) and see what might be going on. Any more ideas? The engine cut off once before, but it appeared to be a fluke and I don't think I made the connection then...but it appears to be getting worse.

Thanks for any suggestions!

Margot

Yaami · 08-22-2002, 11:47 AM

I have an '88 911 Carrera as well that had the exact same symptoms. I replaced the plugs, spark plug wires, distributor cap, rotor, and the DME relay. All failed to solve the problem. I was about to take it into the local wrench, but decided to have one last look-see.

I was looking for vacuum leaks, loose connections, etc. - and I stumbled across a four-pronged connector (it resembles the type of connector on the DME relay) that sits directly behind the drivers-side intake manifold. As I picked up the wire to this connector, the bottom part of the connector fell away. Ah ha! I found my loose connection! I plugged the connectors back together and viola! My baby was back to its old self! No more hesitation or misses!

I hope this is the same fix for your p-car. It's such an easy fix for such a frustrating issue. Let me know if this works for you!

TazerD · 09-04-2002, 05:48 AM

Hello!

I took my car into the shop last week to get temp sensor #2 replaced...I guess it was sending the wrong instructions for fuel, and that's why my car was running really rich--revving up and then flooding itself (maybe).

I've driven 800 miles, not a blip, and the car is awesome!

Margot