BrianRMV

1986 951
The high idle and poor gas mileage may not be related but I suspect that they are. My symptoms are:
- Idle bounces from 800 to 1,100 when cold
- After a couple of minutes the idle settles at 900 +-
- After car warms up the idle is steady at about 1,600
- Turning the AC on will drop the idle to about 1,000
- From a stop power is really low, especially with AC on. After
I'm "rolling" it's not a problem, but I don't get an especially
noticeable boost when the turbo kicks in.
- Perhaps unrelated, but my gas mileage is brutally low. It has
been as low as just under 11 mpg.
- I get what I believe is full boost at slightly over 1.8 bar
- Closing off the line to the idle air control valve will drop the
rpm's but makes getting it started in the morning difficult, and
I don't know what would happen if it's closed off and I start the
AC. Also don't know how that effects general functionality.

What I've done so far:
- Replaced TPS and harness
- Replaced idle air control valve twice
- Replaced dme temp sensor
- Tried a borrowed dme and still had the same problems
- Sent the dme and klr to ECU Doctors and they checked out
"fine"
- I don't seem to have any vacuum leaks
- The wire to the coolant temp sensor looks bad but I don't think
that would cause the idle and mpg issues. Maybe I'm wrong.
- A-Tune. I do have my Weltmeister KLR chip still in but don't
think that's an issue.
- Manual boost controller. I was only getting about 1.4 bar prior
to installing the MBC
- Replaced the MAF about 5 years ago

Any ideas would really be appreciated.

Tiger03447

Check out the connector and the wire thoroughly to the Air temp sensor. You said that you recently replaced that part. If it reads cold Amal the time you the ECM, the ECM will give it more gas and your mileage will suffer. The high idle at start up may be a different critter. Have you checked the MAF lately and checked for drag at the gate?? Hope this helps some .

BrianRMV

It turns out that someone had installed a bogus (for lack of a better term) idle screw. A new mechanic found the problem, replaced the screw, and now idle when warm is perfect. However, when cold the idle is very rough, and will die if I don't give it gas until it warms up. When it's warm and idling properly, turning on the AC will drop the idle and make it cycle up and down.

Also, my MPG continues to get worse. My last full tank dropped to just under 9 MPG. My mechanic suggested having the fuel injectors checked. If nothing else I think it's a good thing to do with a 31 year old car with 200k on any original parts. I also wonder if the MAF could be part of the problem.

Any suggestions would be greatly appreciated. If the problem continues to get worse the car will be cease to function at some point.

alex.rhodes

I had some of the same symptoms as you, buy not quite as drastic. I ended up bypassing the idle control valve and getting rid of the shudder by following the procedure on http://web.archive.org/web/20111230141249/http://www.the944.com/shudderm.htm. My idle has stabilized, i no longer have random stalls when cold and my economy went from 13mpg to 22mpg. Might be worth looking into.

V2Rocket

dead O2 sensor will cause rich running and hunting warm idle.

running rich @ warm idle artificially makes the idle better so the idle screw adjustment may be out of whack relative to where it needs to be for cold idle.

alex rhodes - OP has a 944 turbo which has the later style DME so it does not have the "shudder"

BrianRMV

My O2 sensor was replaced a year or two ago, so I think it's okay.

Alex - do you have a 951? I looked at the link and it seemed to be for a NA, and I did not see anything about the bypass. 13 MPG is about what I generally get now. Sometimes lower but rarely higher.

Thanks for the input.

V2Rocket

was the O2 sensor a plug-in type or a "cut and splice" connector?
if it was cut and spliced it is possible and easy to accidentally get some of the shielding braid in the signal wire crimp...which grounds out the signal and renders the sensor useless.

BrianRMV

I think it was plug-in but I will check. I did not do the install myself. I bought the O2 sensor from LR or Vertex. I had the low MPG issue before it was replaced. It's always possible that both the old and new are bad. It's on my checklist of items to verify.

alex.rhodes

I have an 85.5 944, so the later style DME but it still had the shudder before I followed that procedure. I'm not sure if it will work for a 951, but it worked on the late model 944. We had some of the same symptoms so I threw out my fix.

odonnell

Replace the DME temp sensor. It's $20 and tells the DME how much to enrich based on coolant temp.

You can also unplug the O2 sensor to see what effect its signal has on things. If little to nothing changes, it's probably the sensor I'm talking about. It could be the airflow meter but that's less likely.

BrianRMV

Thanks Alex. This issue has been going on a long time and I've had zero luck fixing it, so I appreciate advice from people who I'm sure know a lot more about working on these cars than I do. I have extremely limited mechanic skills.

The DME temp sensor has been replaced. I believe the harness has been tested too, but need to check into that. It would not surprise me to find out that I have a bad harness, or several, that are making sensors basically inoperable.

BrianRMV

I noticed that when cold, there is a cyclical hissing sound that happens just after the rpm's bounce up. The rpm's even out exactly when the hissing sound stops. This seems to be when the car has warmed up, and the ICV is not longer in play. This makes me think that the temperature sensor is working properly, and signaling the ICV. My mechanic smoked tested the car this afternoon, and says smoke is coming out of the ICV itself. The replacement is used, so I could easily have ended up with a defective one. It has been tested and opens and closes properly. I will probably replace it with a new one, but at $300+ it's a bigger risk than I'd like to take.

Regarding the high fuel consumption, I don't know how much impact this can have, but apparently the fuel pressure dampener is running high (maybe not the correct terminology). I installed the 3 bar fpr with the A-Tune, so maybe this should be expected.

V2Rocket

the ICV in your 951 works at all temperatures for idle...unlike the aux air valve on the early cars which is only for cold starts.

Jfrahm

You do not need a Porsche ISV, a BMW, Saab or Volvo spec part is fine. Under $100.

BrianRMV

Jfrahm -

That would make my day. I don't even want to begin adding up all of my expenses on the car over the last year. I remember seeing a site a while back that cross-referenced parts, but if you have any info on which other ISV's are compatible it would be much appreciated.

Thanks for the info.