Help! 944T hesitation problem

Johns86_944 · 08-23-2002, 05:34 PM

I finally upgraded from my 86 NA to a Turbo (also 86). It has a bad hesitation or stumble at between 1600 and 2000 RPM. The previous owner said it started when he had the engine steam cleaned for sale. It was in great shape and a good price so I bought it anyway.

When accelerating in any gear, or even in nuetral when it hits 1600 the engine goes flat. It does not die but bounces back after the revs drop. This makes the car lurch like a first time stick driver is at the wheel. Same happens when the revs are are the way down and hit 2000. Like I said it also happens in Neutral and is worse when applying the throttle gently. Hitting the gas quickly seems to not cause the stumble. In order to drive the car I must keep the revs above 2000, which means I must rev up the engine to 3 or 4k and slip the clutch a little to take off. Impossible to drive in traffic.

I started by replacing the cap and rotor, (made the mistakeof dropping by the dealer instead of ordering from here because I was anxious), replaced the plugs, checked the connections to the various sensors and injectors, looked for vacuum leaks, but no good. I was going to replace the fuel filter but I can't believe it could be the problem as the car runs great at high speed and will accelerate hard above 2000.

The car has supposedly 75k miles, and only problem I can find is a broken off exhaust stud causing a little leak. (it also has a europroducts stage I chip I'm told if that matters at all)

In reading various posts I see the posibility of this being caused by a faulty air flow meter or throttle position switch. I do not know how to test these though. Any ideas? Whats the chance of it being the computer or some other major $ part?

-John

AFJuvat · 08-23-2002, 07:13 PM

It sounds like your TPS is a bit hosed up - especially sice he says it happened when the engine was steam cleaned.

I'll have to do some looking for the specs. In the meantime, check the following.

Get yourself a few cans of brake cleaner (god I love that stuff!)

Remove air filter, and intake boot, clean/spray out AFM and intake boot with brake cleaner - inspect intake boot for cracks/tears.

Rotate the throttle cam, does it click right as you start to yurn it? if it doesn't, loosen the nut on the adjusting screw and adjust until it does.

Spray the hell out of the throttle body with brake cleaner.

Disconnect the TPS cable (under the throttle body) clean the contacts on the cable and the TPS.

AFJuvat

Johns86_944 · 08-25-2002, 06:17 AM

Thanks, but let me ask you why brake clean instead of carb cleaner? I love the stuff too but never thought of using it in the intake.

I am not sure I know what you mean about the throttle cam and the clicking. When I open the throttle I can faintly hear something engage but it is not immediate, more like after about 30 degrees rotation. Where is the adjusting screw you mention? I see the screw it rests on (Idle stop?) and there looks to be an adjustment screw of some sort in the top center of the aluminium housing.

I found one other problem, the vacuum controled valve that I think lets off extra boost (?) is faulty in that I can blow into it (wont hold vacuum) This is a valve over by the radiator header tank that links (through a smaller 1" hose) the presurized tube going into the throttle to the non presurized intake coming from the air filter. I am not sure exactly what this does, as I have never had a turbo anything before. I don't know if it could be causing the problem, but I need to replace it and notice there are some upgrades available. Someone posted they had replaced theirs with one from a 993. You seem to know a ton about upgrading these cars, what do you think?

Thanks again!

Mike B · 08-25-2002, 06:58 AM

The throttle position switch (TPS) is located on the side of the throttle body...For some reason I can't post a pic but here is a link to one...

http://www.smartcart.com/Paragon/images/944_tps.jpg

When you open the throttle body you should it click almost as soon as you open it...If not then your TPS is faulty...

The Compressor Bypass Valve (BOV) you are talking about is supposed to hold vacuum...This valve holds boost pressure when you shift gears so there isn't excessive lag while your turbo spools back up. Test your valve by removing the top hose and see if the valve will hold suction, if it doesn't, you need a new valve. I picked up the 993 valve as a replacement for mine for about $30...Part # 993.110.337.50

robm-951 · 08-25-2002, 07:08 AM

Quote:

Originally posted by Johns86_944
It has a bad hesitation or stumble at between 1600 and 2000 RPM.

An easy way to test and see it the TPS is the problem is to simply unplug it. Your car's idle will fluctuate aroung quite a bit (because the computer doesn't see the closed throttle contact switch), but if the other problem goes away then you've found the problem.

Rob

Johns86_944 · 08-25-2002, 08:54 AM

Bingo! I unplugged the TPS and the engine will now rev smoothly through ;the 1600 - 2000 range without stumbling. I think a new one is $100 at the dealer, but I have not looked aftermarket. I also have not tried cleaning or adjusting this one as AFJuvat suggested, but based on this "test" is the thing shot or just out of whack?

robm-951 · 08-26-2002, 07:26 PM

Quote:

Originally posted by Johns86_944
but based on this "test" is the thing shot or just out of whack?

Most likely it is shot. The problem with your TPS lies in the closed throttle contacts inside the unit.

Pelican has new ones for $83.00

Rob