Speeddemon944

Hi All,

I am new to Rennlist - but have been lurking for awhile :roll eyes: - I have used "other" forums as well. My family and I have 4 944's from an 87' 944 DD to a 951 SP-3/NASA GTS-3 race car.

I am currently having an issue with my race car here are the details -

89' 951S - Stock motor (has been rebuilt including turbo), Stock DME/KLR

The symptoms

- cold idle is a little rough - not bad - I would deem it normal
- warm idle is very rough (stumbles)
- Revving up I get massive missing and backfiring - I cannot get the car to rev above 3000 without a terrible miss and backfire
- The miss is electrical across all cylinders - verified by a timing light.
- The miss goes away ENTIRELY when the TPS is unplugged

What I have done so far -

- New LR injector, knock, and reference sensor harnesses
- new Fuel filter, pressure regulator and dampener, plugs, wires, cap, coil
- new DME temp sender
- new TPS
- new TPS plug and harness to the DME/KLR
- new vacuum lines
- new reference sensors
- tried 3 known good DME/KLR combos
- Tested AFM - Good
- took apart DME to check for solder joint issues - none

My next thought is to unplug the CV to see if maybe it is acting up when the KLR sends it signals.

Any thoughts and/or suggestions?

TIA - sorry for the PITA 1st post - Mods feel free to move this the 944 Turbo forum if needed.

MAGK944

With everything you have changed and it working normally with the TPS unplugged, it really only comes down to the TPS or something associated with it.

Did you fit the correct new TPS? Na's are different.

Did you adjust the TPS correctly with the micro switch closed?

I'm not sure but I think the IAS is connected to that circuit in the DME. Could the IAS be causing a large vacuum leak and feeding the DME a false reading?

Speeddemon944

Hmm Not sure on the TPS being a turbo one...It was a spare from the garage... I will confirm part numbers using PET.

I believe I adjusted it correctly...I adjusted it so that when the throttle cam moves just barely off of idle I hear the 'click' sound.

I will see if I can find a test procedure for the IAS

Speeddemon944

Ok so I verified the part number is good per the PET

I sprayed some brakleen around the IAC and not change to the idle. Do you still think it could be the IAC. From what clarks-garage says it could cause some of the symptoms I am seeing.

MAGK944

I really am at a loss as to what it could be considering what you have already changed. I would check the ias per Clark's, certainly worth a look down there to see if both of the rubber pipes are secure. DME temp sensor or TPS would have been my first thoughts but you have changed those. Possible your spare tps was also bad?

Thinking logically, tps connected=problem, tps disconnected= no problem, changed tps= same symptoms, it has to be that both tps are bad or you have a bad connection at the tps connector.

mel_t_vin

In other words, you replaced your old used part with another, unknown, old used part.

Any idea if your ICV/IAC is original to the car...25 years old?

Same question re: your AFM...25 years old?

konakat

Test the TPS with a multimeter at the DME connector. If it isn't just a bad TPS, you may need to rewire that connection. Wiring harnesses are failing with age on these cars so new wire may be the answer.

Speeddemon944

I have confirmed that the TPS I swapped was a new "good" one and has the correct Bosch part number.

I dry ran all new wires from the TPS directly to the DME and KLR and the problem is still present. I also replaced the TPS plug.

The ICV/IAC is original to my knowledge. I do not think it is this though because the problem goes away once the TPS is unplugged. If the ICV/IAC was bad then the problem would happen regardless of the TPS being connected or not. Correct?

I did test the AFM but I have not tested the actual harness to the DME/KLR. That will be my next step.

A buddy of mine who runs a Porsche shop also suggested the AFM - He has seen the AFM cause issues that mimic a faulty TPS on cars with OBDII. I know - different animal

michaelmount123

Where are you located?

Speeddemon944

SLC, Utah - A heretic in the land of Zion

Speeddemon944

Any idea what would happen if I unplugged the AFM and started the car?

I don't need to drive it to get the damn thing to miss. Just have to idle until it warms up and then rev it a little.

homerj

i had similar problems on my car. the first time i found the rotor had damaged the cap on car. so i put new rotor,cap and coil. fixed it. next time the tps was set in the wrong location and it fixed it.

Dougs951S

if you unplug the afm the car will probably not idle, or idle really really badly.

Speeddemon944

So I wanted to update you all on what was found.

The bolt that holds the distributor cap rotor shaft to the cam gear was loose.

Not sure why the car would run fine if the TPS was unplugged - but I have driven the car around and it runs great now..

Thank you for all your help and suggestions!

konakat

Could you check out my thread and see if it sounds like it could be the same issue? https://rennlist.com/forums/924-931-...l#post11261644