pointfivezero

Happy Sunday;

I headed out for a 60 mile drive to San Jose this morning but I never made it. About 45 minutes into the drive, while driving at a steady 75 mph, the car began to surge. I was very low on gas but still had four gallons remaining in the tank. I immediately pulled off the freeway into a gas station. By this time, the idle was surging wildly. I turned off the car, filled it up and it started fine. I headed back onto the freeway (heading home) but the surging and bucking started again. I pulled over several times. When I turned the car off and started it again, I could drive for a few miles before the surging started again. Finally, with the traffic getting heavier and the car getting worse, I pulled off in Oakland and called AAA. However, after sitting for 15 minutes, I started the car and it idled flawlessly. I drove around the block a few times and then headed back onto the freeway. I drove the last 20 miles home with no problems. The idle was steady.

I have noticed over the past several weeks that the idle was varying between 900 and 1100 rpm where as it used to be a steady 900.

Update: Just took the S for a 1/2 hour drive. Mixture of surface roads and freeway. Brought it up to full temperature. Absolutely no problems. One opinion is a bad fuel pump or idle control valve. If so, why would the problem only surface after 45 minutes of driving this morning and disappear completely now?

Thanks in advance for any advice.

Tim

MM951

Bump. Same problem as me.

Jeff928S4

When I had my S, I has a problem similar to this.

I couldn't really feel the "surge" unless the car was at idle. Sometimes I would have to keep my foot on the gas at stoplights to keep it from dropping too low. It would bounce from 1100-1300 down to 500 and back up. It was not always there....it had its bad day and its good days. It pretty much always had a high idle, unless it started surging.

You *could* feel the surge when driving, but only when there was no application of the gas pedal. If I was on the highway and let my foot off the gas, I could see the RPM needle fluxuating.

At first I thought it may be bad spark plug wires....nope.
Then I thought it was fuel delivery thing....nope.
Maybe the TPS (Throttle Position Sensor)....nope.

I took my Air Flow meter apart and re-did the arm thing, so it would make a new swipe line.
Info here about this.......https://rennlist.com/forums/showthre...Air+Flow+Meter

...this helped, but didn't fix it completely.

Last resort was the Idle Stabilizer Valve. I tried blowing some WD-40 down the air intake to perhaps "unstick" the valve, but it only somewhat helped. I heard the intake manifold has to come off for this and I figured it was costly. Not really. A local shop swapped out the Valve and it only cost like $150 Canadian...not too shabby.

This kept my idle steady....surge went away.

Luis de Prat

Before plunking down that amount of cash on an ISV (which I don't think would cause the car to buck at all, only to surge), I would try replacing the Ignition Control Module.

Do a search on this part. This little sucker is 16V specific in the 944 cars and wreaks havoc when it begins to go bad. I replaced the freaking AFM unnecessarily because I didn't know about this bugger. HTH.

MM951

Does anybody know if the early ISV is the same as the late one?

7thStranger

If anyone is interested I have a ISV for an S that I used for only 2 months for sale.

I also have an ignition control module for an S that I used for 2 years, about 10,000 miles for sale.

gtroth

I had both problems on my S: idle flopping when cold and "cutting out" when very cold (bad cut-outs cause surging/bucking).

New ISV cured the idle flop 100% (of course I did do a bunch of other stuff while the intake was off).

The cut-outs, I'm still working on. For me it will normally only happen when the car has warmed up and it's below around 10°F, but it won't always misbehave. You might search for my threads. I've done (not all for this problem): plugs, wires, cap, rotor, coil, ICM, ISV, TPS, throttle reseal, vacuum lines, injectors WitchHuntered, FPR, fuel filter, grounds, cleaned AFM connector, checked AFM voltage at the AFM connector, checked all the other sensors at the DME connector...yikes. I'm left with intermittent AFM or speed/ref sensor, I think (although my speed/ref sensor signal looks good on the 'scope..). I can't even determine if it's a fuel or spark issue.

So, you can imagine, I hope you find a solution.

Cars running like a top now all other times, at least.

Luis de Prat

Your AFM may have worn down the coper lining to the point where you get erratic operation. You've read about taking them apart and bending the wand, I suppose? That's an option. You could also "borrow" one from another car for a few days and see if that cures the problem.

A shop did that on my S2 only to find that popping mine back in afterwards the car worked fine also. Dirty connector, like I mentioned. Sorry that didn't work for you. I replaced so many parts before someone told me that tip!

pointfivezero

Idle problem update:

My tech felt it could be the DME temp sensor. When this sensor goes bad, the O2 sensor can send the wrong mapping (cold when the engine is actually up to temperature). This seemed to help the cold idle stumble but I was still getting a surge at idle (from 900 to 1200 and back). Frankly, I have been too nervous to take the car too far from home and relive the "nightmare on 880".

I'm doing the cheap things now.....new air filter, fuel injection cleaner, 76 fuel. I'll be headed out this afternoon for a check/see.

In the long run, I'm fairly certain it will be the Idle Air Control Valve. One bright spot, my mechanic says he can replace it in 30 minutes without removing the manifold.

I'll take all the bright spots I can get with this issue...

Tim

Luis de Prat

Tim, I'm familiar with your problem and have replaced the ISV myself like your mechanic says, without removing the intake manifold, but I really doubt this will solve your problem. At least it didn't work for me. The car kept hesitating and cutting out unexpectedly.

The problem you describe is more symptomatic of a bad ignition control module. You should seriously consider replacing this $50 part before spending $200 on an ISV that you don't need. Heck, if you weren't half way around the world, I'd give you my old one which probably still works perfectly.

YMMV

pointfivezero

Hola Luis....thanks for the note and suggestion.

I went for a spirited (65 - 90 mph) 45 minute drive today with no issues. Was your problem sporadic, as well? Did it only occur after the car was driven for 45 minutes to an hour?

Thanks again!

Tim

Luis de Prat

Exactly these symptoms. Try the ignition control module. Most mechanics who work on 944 cars don't know about it because it's only on the 16 valve cars, like the 944S and S2. It worked for me.

Only other problem I've had since then was a bad connection to the AFM plug.

pointfivezero

Thanks Luis. I just ordered a Bosch unit from Pelican! I'll let you know how it goes.....

Tim

pointfivezero

PM sent.

Tim