georgie

I have a problem on an '89 C4 whereby intermitently and unpredictably I seem to have an engine timing problem or perhaps maybe a problem with the mass air flow sensor?

Symptoms: the car has inconsistent power. Sometimes full on, sometimes 3/4 power, and then sometimes I'll be cruising along on the highway and all of a sudden the car will start badly hesitating and "bucking". It seems to lose all power other than enough power to keep it going at it's current pace; however, like I said, it starts bucking and almost backfiring. Very, very unhealthy feeling and sounding. Then, I'll slow down the speed, pull the speed back up, etc. And after about five to ten minutes usually the problem will go into remission. But it unpredictably comes back. Recently, it has shown up upon starting the car. It barely wants to start, and when it does start it doesn't want to hold idle (dips very low) and there is almost no relation between throttle levels and engine revs.

Any ideas?

Thanks!

Drew_K

The symptoms you're describing are absolutely not normal. I would advise getting your car to a mechanic ASAP to have it checked out. Report back what you're told and we can help you diagnose whether it's bull or a real problem.

To answer your question, the problem could be any number of things, from a weak battery or alternator, broken distributor belt, etc. Whatever it is, I wouldn't drive the car until this problem is resolved.

johnfm

Georgie

have you checked the various 'obvious' things yet? Check the distributor belt - remove & check the caps, check the rotors & check that both rotors go round. Look for arcing (find a dark garage at run the cat in the dark, looking for arcing).

Have you tried a DME reset (ie disconnect battery for 15 minutes)?

Is your car 'dry', ie no moisture /water in the footwells to interfere with the DME??

Adrian

Dear Georgie,
This sounds electrical to me. What are your electrical loads like at the time when the problem starts. I had this happen to me once when I engaged the air conditioning at too high an rpm.
The first thing I recommend is a battery capacity test and a voltage output test of the alternator. At idle the voltage across the battery should be no less than 13.8VDC with aircon off.
Ciao,
Adrian
911C4

PS: The standard 964 engine is fitted with an airflow sensor not a mass airflow sensor. They are quite different.

Fred, Long Island

Sounds all too like my "Ghost" last last year. Turned out to be the DME was fried...possibly caused by faulty plug wires.
The key was that it wouldn't idle. The resonance flapper kept being activated as the brain tried to resucitate it after it was deprived of fuel by that same brain. We watched the DME relay (cover off) contradicting itself.
Ironically, hammering it produced no fault code.

georgie

Would it be safe to assume if it was the distributor belt that the problem would be consistent. More often than not, the car runs fine. Fred's desription of it being a "ghost" is entirely my feeling. I can be cruising on the highway at 70mph and all of a sudden you begin to feel the "ghost" lurking.

Ironically, I've never had this problem occur when the cruise control was on.

Scrooge

Georgie,

I, unfortunately, have exactly the same symptoms as you with my '90 C-4. A shop here in Williamsburg diagnosed it as fuel contamination and proceeded to empty my tank, remove it, flush it, change the fuel filter, and clear the entire system with compressed air. $800 and two weeks later, I find myself still faced with the problem. Is your car currently at a shop, or are you working actively to take care of the problem?

My problems seem to go in phases. Upon start-up, the idle is very low and the car sounds terrible. Sometimes the revs climb to slightly over 1K without any throttle input on my part and fall back down. If I try to accelerate, the car bucks and pulls, only gaining speed intermittantly. As the car warms up, the problems seem to subside, but the car goes through a period during which very light throttle almost kills the motor and causes an extremely rough idle (that unhealthy sound again). Releasing the pedal brings the idle back, and adding more pressure brings the revs up as normal. As you can imagine, this makes a gentle launch difficult and very frustrating. Do you have this problem also? After a while, this symptom ceases as well, and things return to normal for the most part. Really annoying . . .

My mechanic is on vacation until July 8 and the car is supposed to go back in around this time, so perhaps I will know more then. However, if anyone on the board has any other ideas to share, it would be greatly appreciated.

Thanks!

Adrian

Dear Matt,
First thing to do is a DME reset. Disconnect the battery leave off for 20 mins. Reconnect and start up. Let idle for around 2 to 3 minutes and then go for a good 15 minute drive. Once you have done this please report back. The archives are full of this problem and all 55 plus potential causes.

If the reset doesn't fix your problem we need to look at the air intake side. The accelerator pedal operates the air system. Low idle more often than not means not enough air.

Is your 964 stock standard before we go any further? if it is try this after the reset. Remove the airbox cover and filter and with your hand put it in the airbox and check for oil contamination. If you have a K&N filter installation do the same.

The process of fixing these problems is a caseof elimination and I always start with what is most common. Obviously your mechanic does not.

Ciao,
Adrian
911C4

GMS

There is also one thing to check; early 964 air flow sensor wiring had an update to prevent the connector between the sensor and the harness being strained and causing poor contact.
If this has not been done, and there is a TSB, then you should do it.

We have had cars with strange running problems that seemed to have no relationship with this connector but carrying out the repair as described in the TSB cured the fault.

A faulty battery could certainly be the fault too.

Scrooge

I have completed the DME reset procedure, but to no avail. In fact, while on my spirited 15 minute drive, the car was acting so poorly that I had to pull off to the side of the road. While in-gear, I was giving the car gas and yet the revs were still dropping. After idling for a while on the shoulder, I was able to drive off and get back home with only minor shuddering. I have also found no oil contamination in the airbox.

The car is completely stock, not even a K&N air filter has been installed. I tried swapping DME relays with my spare, but this too failed to do anything to solve my problem. What next?

DaveK

Hi,
You should check the airflow sensor wiring TSB that GMS mentions, since it could be that.

Have you had a hammer on it yet? The problem could be logged as a fault and this would make finding it very quick. Most places will plug the hammer in for little or no charge.

I once had a problem where my car started "bucking" - like it totally lost power for a split second and then came back. It did this several times over a few miles and I pulled off to the side of the road - at which point it stalled. It would then turn over but not fire.

Turned out to be my flywheel position sensor. Mine had died completely (actually, it fell off....) - it's a long shot but perhaps yours is intermittently failing.

But I think the first thing to do is get a hammer on there and see if a failure is reported.

91C2wrencher

Hey Matt, Since your still flogging this one around I'll toss in my $0.02 worth. Some time last my car started bucking and hesitating much like you describe. My pro-wrench poked around for a few days and the only thing he could find was two very lose spark plugs. He tightened'em up and no more problem. He explained it as messing up the firing circuit(spikes and transients) and cauing confusion in the DME. Have you checked that toyur plugs are snug?

Carl Muckenhirn

My '89 was running pretty much the way described. After cleaning the ISV and a new set of plugs its mostly there. Still a little funny at idle, but I think I've got it down to the ISV not being properly re-attached. Seems they pulled it out to clean it without replacing the hose clamps. I can smooth the idle by sealing the slight gap between the hose on the intake side of the ISV.

Also, new plug wires wouldn't hurt if they've never been changed, it fixed my PDAS/ABS problems. Not that expensive, but a PITA to change.

carl.

georgie

Sorry I've been out of the loop for the last few days here. My car runs EXACTLY the way Matt describes. Bucking and studdering, sometimes not starting. Idle totally messed up at times. No throttle response at times. This more often than not occurs when the car is cold. However, a couple time, DRIVING TO WILLIAMSBURG ACTUALLY (maybe it's something in the air there on Rt.. 64, it started bucking and studdering as I was going 75 miles per hour in a pouring rainstorm. I thought I was going to have to pull over and be stranded there. However, I kept going....the car seemingly had just enough power to keep it at the cruising speed, but was lurching and bucking...literally feeling like the car was coming apart. It was miserable.

I tried the DME reset. Made no difference whatsoever unfortunately. A friend of mine suggested the air flow sensor may be contaminated somehow. Does this make sense?

It's so, so frustrating as sometimes I'll take the car out and it runs perfectly. The next time for example, it will have "half power" .....like you jump on it in second gear and there is just nothing there. The revs increase but there is just not the same horsepower. So, in this case it goes beyond the throttle response seemingly. Sometimes the car seems down on horses about 25-30%. A friend of mine that owns an SC drove my car recently, and said, "What a dog. They must have made these C4s much more civilized."

What is the ISV? I don't know this anacronym.

My 89 C4 is completely stock including all filters. It only has 50K miles. I purchased the car two months ago and it ran fine. Now with 2K more miles on it, it often runs like a dog.

The first time this problem we're all trying to identify happened to me, I was at a stop light....the light turned green. I got on the gas and the car started back firing, and I could hardly make it up a moderate hill in first gear with my flashers on. I thought the thing was going to blow up. I pulled over and it smelled like something was burning. I got under the rear of the car and the exhaust was putting off a grey smoke that typically is not there. Like a condensation smoke , but the car was hot.

My gut was that the mixture was all wrong on the car. Like the car was "choking".....getting too much fuel and not enough air. As Matt describes, I thought it was a fuel problem...so I ordered a new fuel filter, but have yet to install. But my gut is it's something in the ignition or like I said in the mixture setting or maybe even in the timing settings.

Ideas?

Sorry, I'm late to the party in the discussion given that I started the thread.

Thanks!!!!!!

georgie

From Matt;"Upon start-up, the idle is very low and the car sounds terrible. Sometimes the revs climb to slightly over 1K without any throttle input on my part and fall back down. If I try to accelerate, the car bucks and pulls, only gaining speed intermittantly. "

This EXACTLY OCCURS in my car as well. It is so odd, how the revs take on a life of their own....rising to about 1500 and then falling back down. But always just up to about 1200-1500, never higher.