slickwilly

I have been experiancing some missing and hestitating problem for the last year 3000-4000 miles. It is real noticable a low rpms( <3000 rpm). It shakes a little when at idle also. When driven under load it is real bad until reved to above 3000 rpm.. Motor seems to get very hot although the oil temp doesn't show it. It fires up ok when cold however It is very hard to start when hot. Takes alot of cranking to get it to start.

Here is a list of what I did I have check, replaced, cleaned.
1. Fuel filter was replaced.
1. Checked for codes. None.
2. Inspected the distributor belt. Not broken.
3. New caps, rotors, spark plugs, wires, coils.
4. Moved tail lid ground strap away from coil leads.
5. New o2 sensor.
6. New DME relay.
7. Techron gas treatment and dry gas.
8. Cleaned ISV and air flow sensor.
9. Fuel filter replaced again. Black junk was leaking out of it when I removed it. So I decided to cut it open and check it out. I found a brown sugar like substance in it. It dried to a fine brown powder.

So I am going to check the fuel system. Starting at the tank and fuel pump and working toward the fuel pressure regulator and injectors next.

Does anyone have any other things I should check or try? Getting ready to throw in the towel and bring it somewhere but would rather figure it out on my own.


Thanks,
Bill

93 964 C2 Cab

Eric Kessel

Did you do anything to test for air leaks? At open throttle (higher revs, quickly), the DME ignores the air flow sensor, but when other than open throttle, air leaks could be causing all kinds of problems....... Just a thought...... (did someone put sugar in your gas tank?)

RallyDogRacing

You can try some old school tests for finding vaccuum leaks by getting the engine running and up to temp, then spritzing brake-clean or starting fluid at suspect spots around the intake. Revs go up and you're in the vacinity of the leak. Carefull, don't dowse the whole thing and go up in flames; take your time and you might find a leak.

The cold start system may compensate for the leakage based around the added fuel in the temp profile. The other thing would be to verify the TPS is sending the correct signals and that your idle and WOT switches are functional. I don't know if in the 964 it's a single unit doing all (idle on/off, potentiometer, WOT on/off) or sep units. I'm sure someone does. I does however sound air related based on your description. Good luck.

Rob Dupree
1990 C4
1990 Audi V8
1997 Toyota 4Rnr SC'd

slickwilly

Thanks for the quick responses. I will let you know what I find.

-Bill

springer3

Get the diagnostic codes read. The cylinder head temperature sensor could be signaling "very cold". That would keep the cold enrichment on, causing lumpy idle and difficulty with hot starting. I believe, however, that the DME is programed to recognize a bad temperature signal.

slickwilly

Quick Update: I replaced the fuel injectors and drained and flushed the fuel tank. Runs like a champ. I am going to watch where I fill up from now on. Hope this info can help someone else out down the road. Thanks for all the suggestions.

Colin 90 C2

In response to what MadHungarian said about the spritzing. It's a great idea but please spritz with water. I know that the cleaning fluids evaporate, but the water spritz is a little less dangerous and if any gets in the system, it will act like a water injection and maybe clean up your intake valves.

ChrisO

Had the same situation in my C-4. It turned out to be a "rubber bumper" that the air box sits on. It was a $ 2.50 part and took about 15 mins for the mechanic to fix. The bumper had come off and cause the sensor to read wrong. After replacement, it was perfect. Hope this helps.

puma1824

Did you ever figure out what's going on? I seem to have somewhat of the same problem. Kinda weird since I just purchased and PPI checked out.

burgass

Bill
How did you flush the tank?

Jerry Garwick

Bill

How did you cut your filter to inspect the internals?

slickwilly

Puma1824, It turned out to be clogged injectors.
Burgass, When I had the fuel pump off for draining the tank I poured more gas into the tank to hopefully flush any remaining dirt/garbage out.
Jerry, I just used a hack saw to cut it in two. I was quite suprised to find so much dirt trapped in there.
HTH!
-Bill

puma1824

I guess the injector replacement was expensive. Roughly how much?

slickwilly

A little over $600 for new ones. It is quite inexpensive to have them cleaned( $72 + shipping). I should have done that but I wanted to have the car back on the road ASAP. I am going to have the clogged ones cleaned one of these days so I have a spare set.

puma1824

Are they hard to replace yourself, or did you have a shop do it? Engine drop required?