I've been struggling with this for a few months now, and have searched these forums with no success. Maybe I'm searching for the wrong thing.
I have a '98 Jetta, AHU engine, 317,000 miles. No modifications. The problem happens when it's been sitting overnight or all day, in temperatures up to 50 F. It hasn't been warmer than that since I noticed the problem.
I start the engine and it will idle just fine. I can run through the gears without touching the throttle for a half a mile or so and the problem will not happen. I can drive away.
If I get the revs over 1500 (20F or below) or over 2500 (40 or 50F) the engine starts running really rough. If I don't let up on the throttle, it will die. Then it's hard to start. Lots of cranking with lots of nasty, fuelly fog coming out of the exhaust. It will eventually start, and run OK. Once it's been running for a few minutes, everything is fine.
Even if I'm not moving, I can produce the problem just by gently pressing the pedal. It's almost like the engine floods.
I can't see anything unusual on VAG-COM. The intake and coolant temp sensors look normal. The fuel temp comes up in a fashion that looks normal to me. I'm not sure what to look for.
Stuff I've tried:
*Replaced fuel filter and thermostatic tee
*Replaced injection pump with a rebuilt one from Boraparts
(yup, I'm an expert at timing belt changes with VAG-COM, the timing is right in the middle.)
*Replaced nozzles about 120,000 miles ago. I took them apart recently and cleaned them up, along with the injectors.
*Tested the glow plugs (even though the engine starts quick)
*Re-checked the little hose in the ECU (it had a crack in it about 200,000 miles ago)
I'm still suspicious of the injectors, but before dumping $1000 into some rebuilt ones, I'd like to be a little more sure.
I'm hoping this is such a common problem that no one even bothers to ask here.
I have a '98 Jetta, AHU engine, 317,000 miles. No modifications. The problem happens when it's been sitting overnight or all day, in temperatures up to 50 F. It hasn't been warmer than that since I noticed the problem.
I start the engine and it will idle just fine. I can run through the gears without touching the throttle for a half a mile or so and the problem will not happen. I can drive away.
If I get the revs over 1500 (20F or below) or over 2500 (40 or 50F) the engine starts running really rough. If I don't let up on the throttle, it will die. Then it's hard to start. Lots of cranking with lots of nasty, fuelly fog coming out of the exhaust. It will eventually start, and run OK. Once it's been running for a few minutes, everything is fine.
Even if I'm not moving, I can produce the problem just by gently pressing the pedal. It's almost like the engine floods.
I can't see anything unusual on VAG-COM. The intake and coolant temp sensors look normal. The fuel temp comes up in a fashion that looks normal to me. I'm not sure what to look for.
Stuff I've tried:
*Replaced fuel filter and thermostatic tee
*Replaced injection pump with a rebuilt one from Boraparts
(yup, I'm an expert at timing belt changes with VAG-COM, the timing is right in the middle.)
*Replaced nozzles about 120,000 miles ago. I took them apart recently and cleaned them up, along with the injectors.
*Tested the glow plugs (even though the engine starts quick)
*Re-checked the little hose in the ECU (it had a crack in it about 200,000 miles ago)
I'm still suspicious of the injectors, but before dumping $1000 into some rebuilt ones, I'd like to be a little more sure.
I'm hoping this is such a common problem that no one even bothers to ask here.