The Reverend

I had a short day at the CA Speedway last weekend and noticed the engine was acting up a little towards the end of the day. I didn't think anything of it because it's done this in the past after track days and then just clears up after a few minutes of regular driving. I didn't drive the car much after that, but basically the condition continued...

Symptoms:
- lots of hesitation (sometimes it's sluggish, sometimes it completely stops accelerating and then starts again) under relatively random conditions (part throttle or full throttle, high rpms or low rpms)
- sputtering
- some backfiring under light throttle or while decelerating
- occassionally low idle and has died at a stop once so far
- check engine light came on after a while. there were two codes, both for the car being "too rich." I erased the codes and have not gotten any codes since (after 8 miles of driving).

I replaced the spark plugs and that didn't fix it (the new plugs have pretty normal color so far - a little on the black side). I set the coilpacks up on the head and all four sparked properly when the engine turned over.

We were thinking O2 sensor, but as I understand it, that should not be an issue under full throttle and there was no code pointing to the O2 sensor malfunctioning. We are now thinking possible fuel delivery issue and we're going to be checking fuel pressure next.

Any other suggestions? UL - you got any ideas?

geminiS2

MAP sensor??????

The Reverend

Shoulda thrown a MAP code at the ECU, no?

Elistan

Try unplugging the MAP sensor and re-seating the connection. Smack it with a screwdriver handle a couple times, too.

ultimate lurker

I agree with the MAP sensor. Mine only started acting up after 30k miles and it has never thrown a code when it screws up. It still provides an input to the ECU, it just doesn't represent reality :-). The wrong input could result in a rich or lean condition.

Smack that bitch up ;-)

UL

p.s. - just had a TPS failure on my car at 37k miles. Wierd.

The Reverend

[QUOTE]Originally posted by ultimate lurker
[B]I agree with the MAP sensor.

Strike

[QUOTE]Originally posted by The Reverend
[B]

Really?

John MI blk/blk '01

Is it possible that a little oil has backed up into the throttle body through the breather tube? I would take the intake inlet off and see if that is the case. This could give you a bad reading,no?

mas

Just a few ideas:

fill up the gas tank & add some Chevron Techron or STP Concentrate.

Check the throttle cable and make sure it's not too tight or too loose

Take off the MAP sensor, clean up the O-ring & the plastic contact areas, then put it back carefully.

Double check the fluid levels, specially oil and coolant.

Reset the ECU

PS: When the O2 Sensor fails, it normally throws a code and even with the code the car should run fine, it just goes back to the pre-programmed valued.

The Reverend

You guys rock! I took the MAP sensor off, smacked it, cleaned the o-ring, put it back on and drove it - seems fine now. I feel like a dumbass for dumping $150 on an OBD-II scan tool... but I guess I'll be able to use it in the future.