'91 Fox Won't Idle Cold

[Bryan Eastham]

I have been wrenching on VWs for a long time but this one has me stumped. The car will not idle when you first start it. It takes a lot of cranking to get it started and when it starts it runs rough for a few seconds and then dies. If you start it 20 times and let it run for a few seconds each time untill it warms up it runs fine but has no power on excelleration. I have done cap, rotor, wires, and plugs. I have checked the timing, cold start valve, and all 4 injectors for spray pattern, leaks etc.. I replaced the coolant temp. sensor and the fuel filter and nothing has changed.

I have had this car since '92 and have had all of the usual stuff break and wear out but this happened suddenly and has me beating my head against the hood! Any ideas would be great!

[boschmann]

Hows the fuel pressure & the fuel pressure regulator?

[Bryan Eastham]

I was hoping to solve this one without having to take it to a shop but after reading up on checking the fuel pressure it looks like it takes a specialized guage. I have a spare pressure regulator and a spare accumulator from a car i parted out so I might try both those first. I replaced some vac. lines and swapped out the aux. air (idle air?) valve over the weekend and still no change.

[boschmann]

A '91 Fox should have an AFC Digifant II system, not the older CIS-E mechanical FI system that requires special gauges. Any simple fuel pressure gauge will work. There is a small bolt plug in the end of the fuel rail, remove it & slip the gauge's hose over the fitting. Pressure should be 35-40 psi running & rise to around 45 with the vacuum hose disconnected from the fuel presure regulator (opposite end of the fuel rail). After shutting down the pressure should not drop below 29 psi after 10 minutes. That would indicate a stuck open injector or bad regulator.

[Bryan Eastham]

This car was an early '91 and is identical to the '90. It has the mechanical (CIS) and individual injectors. Wiring, engine, body etc. is all '90.
From the shop manual and the Haynes manual it looks like the CIS system needs a flow through pressure guage with an on off valve and the correct screw fittings for the system.

[boschmann]

Sorry to hear that, the AFC system is much easier to diagnose.

[noodle32]

Have you checked your electronic fuel injection fuse? I had this problem all winter (starting and stalling - pressing the gas manually and letting it intake in a pattern until the engine would finally pressurize it's air/fuel ratio - I checked everything from the cold start valve to the fuel accumulator - nothing until I realized that this one little fuse on the fusebox for the electronic fuel injection was suspected to be the prob - replaced it and haven't had a prob w/ it since - VW fuel systems are pretty strong and durable - I think the only thing I've had to replace on my Fox was the fuel filter as far as the fuel area goes - so check this out hopefully it should solve the prob - good luck!

[vwsmp]

i had the smae problem and ended up spending $400 fixing it. but all it was for me was the vacuum hose head split at the connection to the vacuum advance housing... try that. sean

[noodle32]

You may need a new auxillary air regulator - this allows your car to idle quicker when cold as the engine heats up - it's connected to the side of the engine block under the intake boot - (you'll need to remove your boot and some hoses under that to get to it) if the metal plate inside that electronically heats via the cold start valve signal to open the ports attached to allow extra air to bypass the throttle body and allow the engine to breathe directly through the intake - if you go to any search engine and just type like 'vw fox auxillary air regulator' (that's the exact name of the part - it should be able to find one for you - the same thing happened to me before I replaced mine - I actually cleaned out the intake and somehow the cleaner caused whatever that was left of the metal plate in the AAR to not work anymore - which led to no idle @ all until I replaced it - hope this helps - it's a pretty good guess for this part is known to go bad after about 10+ years - (symptoms being the idle gets slower and slower over time despite the amount of throttle put on the car)

1990 VW Fox Coupe (Under construction)
1988 VW Fox Sedan (R.I.P)

[Bryan Eastham]

I replaced the aux. air reg. already and there was no change. I am looking at replacing the fuel injection relay at this point.