Runs Rough When Cold

jmd_forest · 05-05-2008, 10:47 AM

Just got our 86 944 NA on the road after a long "rehab". It runs pretty good when warmed up but rather poorly when cold. When cold It will stall if you give it a quick depression of the throttle and seems to have little power. If you ease into the throttle it will rev up though. I've already done what I think are the obvious culprits: replaced spark plug wires, replaced fuel filter, replaced DME Temp Sensor, replaced O2 sensor, quadruple checked valve timing, checked all vacuum lines by squirting all lines, connections, and gaskets with starting fluid. I ran the Clark's Garage O2 sensor test on the new sensor and it seems to always indicate rich (.965V) even when purposely inducing a vacuum leak (but it also ran poorly when cold before replacing the O2 sensor). The car does not smoke at all, cold or warm and it starts right up.

I'd hate to take it to the local German experts with so many 944 specific experts right here. Any ideas that could point me in the right direction?

jmd_forest

bholmes · bholmes's Garage

Sounds to me like you just forgot the joys of brute 944 power LOL

really though, maybe try checking the AFM, clarks has a how-to on that using just a volt meter does it only do it when it's cold though?

kdjones2000 · kdjones2000's Garage

The O2 sensor is out of the DME circuit until the car is warmed up, at least until the O2 sensor is.

What may be happening is that while running in open circuit mode, your O2 sensor is not allowing the DME to adjust A/F ratio (Car is running on preset maps at this time), but once the sensor is in the circuit, the system is compensating for whatever is out of spec.

I would look at the AFM and TPS'es and see if the resistances are in spec and that the barn doors are not stuck.

Good luck,

Keith

jmd_forest · 05-06-2008, 03:18 PM

Yes, it run poorly only when the engine is cold (it doesn't matter if the ambient temp is cold or warm). Per the Clark's Garage test, the O2 temp is reading rich all the time, at least when the car is warmed up since the test procedure requires the car to be warmed up first. (reads .965V even when a vacuum line is pulled). I'll check out the AFM and TPS as noted but ti runs pretty smooth (although rich according to the O2 test) once warmed up.

Anyone have the specs/procedure for AFM and/or TPS testing?

jmd_forest

jmd_forest · 05-08-2008, 03:04 PM

AFM and TPS check out OK. Swapped the old O2 sensor in and it reads nothing but LEAN (The new one reads nothing but RICH). I swapped them back and forth several rimes just to make sure I wasn't dreaming this stuff up.

Also ran the fuel pressure leak down test and that passed with flying colors so at least I know the injectors are not leaking gas and making it rich.

I'm starting to think the idle control valve is stuck shut??

Any ideas?

jmd_forest

KY944S · 05-09-2008, 01:38 PM

If it's worse wen it's cold out then I would go with the Idle cont. valve. It's a temp fix but you can clean it out (oil does build up in there).

jmd_forest · 05-12-2008, 08:47 AM

Found it ! The TPS was misadjusted. My original check of the TPS was by ear...listened for the click at both ends of the throttle. I finally put a DVM on it and the idle switch was always open. The PO had adjusted the idle using the idle cam stop. I backed off the idle stop 1/2 turn and the DVM started buzzing (switch closed). Started it up and idle was smooth and acceleration from idle was smooth.

jmd_forest