2.5L ('98-'01) Engine bogs down with throttle increase,

[Leigh]

I'm having to "tease" the throttle a little at a time to get up to speed, without bogging down. Happens in all gears/ speeds.

Replaced Fuel pump & Filter, have 65 PSI at the rail.
Treated with multiple injector cleaners
Replaced MAF Sensor, TPS, IAC Valve, EGR Valve, PCV Valve. & intake Air filter.
No vacuum leaks as per Smoke test.

Took it for another road test with an OB2, and it hesitated as always but this time also revved up on its own with throttle backed off. It's done that before and then stopped doing it but this time I got a P0500 VSS Circuit Malfunction code.
Since the rev-up is intermittent, no way of knowing whether it's actually a faulty VSS, or if the Code is generated due to something else causing the rev-up, and I'm fed up with throwing parts at it to no avail!!!

Got another of many previous P1506 IAC overspeed error code's but I've tried 3 different IAC Valves, and yet the same Code keep's coming.

Maybe it's time to junk this piece of crap, and seek an older model with a good old, reliable carburetor.

 

[franklin2]

I would pull the battery cable off to clear the codes, and try again. If the VSS code comes back, I would look into it a little closer. They live underneath the vehicle with the wiring usually in harms way or corroded. The computer uses different control strategies depending if the vehicle is moving or not. It may be confused on that point.

 

[SenorNoob]

The only thing I can think of is a fuel soaked EVAP canister or leak in that system.

 

[Leigh]

Though I had my doubts about the new MAS being defective, in desperation I thought I'd try another one, but to my surprise, it cured the idle problem, as it is now controlled by the IAC Valve, and does not stall out, or overspeed.

The poor acceleration problem still persists, however. It doesn't bog down as much as it had but still is far from spontaneous.
Now I wonder if my luck was so negative to have purchased both a defective MAS, and a defective TPS???
I guess I'll have to give it a try.

 

[RobbieD]

New replacement parts, the quality has seriously gone to hell.

It's like, in order to not waste time, you have to buy three in hopes of finding a good one, and then just returning the other two.