Problems running while under load.

[NakedAssaultGerble]

Car will idle and rev just fine as long as it is parked, but while out driving around it will randomly start to hesitate and run poorly under all throttle positions and begin overheating, then it will randomly stop and be fine again.

I have replaced the radiator, thermostat, water pump, timing belt, crank positioning sensor, o2 sensor, and afm. After replacing said parts it ran fine for about 3 days (200-300 miles of driving) then the problem resurfaced worse now sometimes even causing to care to sputter like it is going to die while idling. All problems occur only when the car is warmed up.

I am at a total loss here I have checked for vacuum leaks, head gasket issues, and while doing the timing belt checked the plugs, wires, cap and rotor (cap and rotor had minor signs of wear but no serious deterioration). The thing that really gets me is why would it clear up after replacing all those parts just to come back a few days later. (On a side note unplugging the o2 sensor, or coolant temp sensor will cure the issue entirely)

[E30_fiend]

TPS sensor could be a likely culprit


Taylor

[jlevie]

Unplugging the ECT or O2 sensor will cause the DME to into open loop and command a richer mixture, which might compensate for intake leaks, low fuel pressure, or dirty injectors. The first thing I'd do would be to have a smoke test run to check for intake leaks and check the rail fuel pressure.

[russhixmo]

I'm going wit what jlevie said

[NakedAssaultGerble]

TPS sensor could be a likely culprit


Taylor

Ohm'd it out this afternoon per the Bently it is within specs.

Unplugging the ECT or O2 sensor will cause the DME to into open loop and command a richer mixture, which might compensate for intake leaks, low fuel pressure, or dirty injectors. The first thing I'd do would be to have a smoke test run to check for intake leaks and check the rail fuel pressure.

All of those things would cause issues while the car was idling not just under load and would be a consistent problem wouldn't they?

[E30_fiend]

here's a thought, have you checked your engine grounds?? I had a friends car idle weird and it turned out that the ground strap from the hood to the chassis and the block to the chassis were both broken and not connected. New ground straps and he was back in business with no problems.


Taylor

[Ryann]

The first thing I would do is change my fuel filter.

[russhixmo]

The fuel filter being clogged would make it idle lean I believe and it would idle around almost 1000, had a clogged filter in my car and that's where it sat, I'd say throw a compression or leakdown test on it and see what u get, also check to see ur air meeter door isn't sticking at any point, the springs do go bad in them and dirt gets under the door and makes it stick as well, best of luck

[jlevie]

The fuel filter being clogged would make it idle lean I believe and it would idle around almost 1000, had a clogged filter in my car and that's where it sat, I'd say throw a compression or leakdown test on it and see what u get, also check to see ur air meeter door isn't sticking at any point, the springs do go bad in them and dirt gets under the door and makes it stick as well, best of luck

If the filter is clogged enoungh it would affect idle. But the fuel flow is much lower at idle and the filter could be clogged enough to affect high speed operation but not idle.

[jlevie]

All of those things would cause issues while the car was idling not just under load and would be a consistent problem wouldn't they?

They might affect idle, but the affect might not be noticeable. The DME is adaptive and can compensate for moderate A/F upsets. Run the smoke and fuel system tests and then you will know if there is a problem there.

[Ryann]

the fuel flow is much lower at idle and the filter could be clogged enough to affect high speed operation but not idle.

Yup.

[NakedAssaultGerble]

Turned out that the new generic 4 wire bosch o2 sensor I bought was defective, the coolant temperature sensor had a hairline crack in it, and the grounding strap at the bottom of the motor had a nick and was grounding out on the power steering pump.

Thanks for all the suggestions I appreciate the help.

[E30_fiend]

Glad to see my suggestion was checked. People often don't associate idle problems with grounds. It's simple really. If you have a bad ground, its just like having a bad power wire.


Taylor

[NakedAssaultGerble]

Glad to see my suggestion was checked. People often don't associate idle problems with grounds. It's simple really. If you have a bad ground, its just like having a bad power wire.


Taylor

Yeah I didn't even think about the ground in the engine bay being jacked up but sorting it out completely eliminated the remainder of the problems I was having thanks for the suggestion :pimp: