DarylJ

Been chasing this issue around for a couple of weeks now and its not getting any better - actually its getting a bit worse. Wanted to see what other people thought.

When I get in the car and its cold or nearly cold I start it (which goes just fine) and it idles just like it always has. Then I try to drive away and it feels like it's down to 1/4 power - sometimes it almost sounds like it missing on a cylinder. If I keep on the gas, it will eventually throw me back in the seat and take off like its supposed to. Put it in second - same thing usually, but not quite as bad. And now it's doing it in third a bit. Then I go down the road for about 60 seconds, and it doesn't happen again.

Since this started, I changed my plugs, wires, cap and rotor. While they did make things much smoother at idle and while romping on it, they had absolutely no effect on this issue.

So I'm thinking TPS. I've tried shifting from first to second (after it gets its power back) without getting all the way off the gas, and I think that keeps it from bogging down in second. So I'm thinking that the closed throttle position of my TPS is sticking until it gets exercised a few times/warmed up.

So, my questions:
- Sound like reasonable logic?
- Am I correct in thinking that when the TPS is showing closed throttle it's on an idle map and will run like the crap I describe
- If I just unplug the tps, will it default to a different map? I understand the your idle/return to idle may suck with it disconnected, but I think that might be a good test for this one.

bearone

unplugging the tps takes the dme out and it doesn't know if it's idle/accel/decel but will run, just not as responsive.

have you checked the basic idle stop screw setting, do you hear the click of the tps as you open the throttle? either could not be adjusted correctly.

fwiw:
i have a couple of stop signs/speed bumps before i get out of the development and keep it in 1st gear/2500, until leaving the 2nd stop sign, where i run in 2nd gear 'til the next stop sign/another 1/4m, which gets me on the main road.

the water temp comes up and seems to help and a colder oat aggravates the situation.

just some ideas.

87951

jpk

Look for a vacume leak. Much of the cold start system depends on vacume. If it were a TPS problem, it wouldn't just be on cold start.
If you still have the original vacume lines in th car, it wouldn't hurt to replace them all. The silicone line kit from Lindsey makes it very easy.

DarylJ

LOL...did that too. Didn't help - but it was due for a replacement anyway.

DarylJ

I resealed the throttle body about 3 months before this started, and made sure that the TPS was making all the right noises. I verified that again yesterday.

As far as the idle stop screw, how would I check that? Using the procedure for jumpering the DME plug in the engine compartment to take the ISV out of the mix and setting idle? Or is there something else that I should try?

Thanks for the ideas!

RMills944

Have you tried the speed/reference sensors? This was my biggest problem with the car when I had a stuttering issue.

DarylJ

Nope - I though they were pretty much go/no go. Thanks for the pointer. I'll see how they're looking.

bearone

when the throttle is closed the butterfly should be close to vertical.

the idle stop screw should be run down until it touches the plate and then a further 1/4 turn, then tighten the jam nut for the basic idle.

clarksgarage has a pretty good reference of what resistance you should see when the throttle is closed, just opening(the click) and open. from 0 to infinity

if it's not set right it can cause problems.

DarylJ

I'm pretty sure I followed the Clark's procedure when I resealed it. Of course that doesn't mean it hasn't crept out of adjustment because I didn't tighten things properly, so I'll go over that on again.

Thanks

quinnfiske

If your problem goes away when it warms up, why not check the DME Temp sensor? These are about $20. They richen the mixture for a cold engine. You can check resistance with hot and cold coolant (I think Clarks has the values as does the factory Test Plan). There was someone else on here who had a similar problem and that fixed it.

DarylJ

That sounds like another good one to try. I didn't realize that "warmed up" could be so soon (I mean - we're talking 60 seconds or so) but I guess that makes sense when the outside temp is 80+.

Thanks - that's also on the list for this morning's wrenching.

N3542

Hey DarylJ my car is doing exactly what yours is doing and I cant figure it out. So if you find what is the cause I would love to know. 1986 944 N/A
Do you think it could be the O2 sensor?

DarylJ

Doubt it - but its a possibility. I can't get mine out. Got the pipe cherry red with a torch and got it to move, but it just spins. I don't want to mess with it anymore until I'm ready to drop the exhaust and fix it properly.

I suppose its easy enough to disconnect the o2 sensor and try.

I haven't tried the suggestions I've gotten yet - the F150 was feeling needy today and I figured I better make sure it's running OK before I go and break something else on the 944.

944CS

my 83 has that hesitation, i believe it is when the DME switches from open to closed loop. I always notice the hesitation right as my air/fuel gauge starts working

FRporscheman

My 84 does this too, for maybe 10 seconds. It's very annoying. It has a new O2 sensor, new plugs, distributor cap/rotor, some other little stuff. It runs perfectly after the first ~10 seconds though.

I bought a new temp sensor but I have been lazy about putting it in.