partial throttle surge

[Garrison]

Hello all,

Getting my legacy and license back today I finally got to drive on the open rode and something I noticed immediately troubles me. When I'm in a gear (doesn't matter which), giving only slight throttle the car bogs. When I depress the pedal further, it then lurches and goes forward, almost as if something is holding it back for just a second.

I assume this to be related to vacuum lines, but the car isn't throwing any codes. Only fuel mod is a Walbro 255 fuel pump, and it has an ebay special air intake.

Can anyone offer some advice? I would greatly appreciate it.

Thanks!

[anothernord]

Possibly vacuum leak, or dirty MAF. Check for leaks, clean the MAF, then reset the ECU and try again.

[goodnight1985]

Bad gas, especially if the car sat (which it sounds like it did). Make sure the fuel pump and filter are clear as well.

If those aren't it, check the basics: Air filter, vacuum leaks, sticking parking brake, plugs, wires etc...

[Garrison]

Filled up with fresh fuel, carb-cleaned the throttlebody and poured seafoam through the PCV and into the gas tank. Problem is diminished but not gone.

A friend mentioned the tranny-mount bushings being shot. Would this have any impact?

Thanks

[Garrison]

ECU has been reset, vishnu method (30 minutes "-" terminal detached with brake depressed for 10 seconds).
I'll drive it to work tomorrow and hopefully the problem with be gone.

Question: How long does it take for the emissions sensors to come up? I'm missing 4 at the moment (pre-reset as well)

[Garrison]

Cleaned MAF today and drove, still only moderate improvement. 5th and forth are where it is most noticeable. Did a once over on everything and didn't see anything out of the ordinary. Sparks look fine.

[Garrison]

This car is a f*cking headache. P0420 came on for the second time today, so the cat is shot. Also, I'm guessing fuel impurities are the reason for the chugging of the engine (now mostly noticeable in 5th and not so bad in other gears). Looking for suggestions as to the strongest fuel system cleaner.


EDIT: Also, is replacing the catalytic converter with a high-flow from OBX a "no-go" as far as CELs, Inspection, Noise, etc?

[Garrison]

problem is now more intermittent, lending credibility to the bad gas hypothesis. bump for an answer to the previous post's question

[ouch1011]

Don't condemn the cat until the engine is running correctly. If the engine is running poorly, it will reduce cat efficiency, and trigger a CEL.

To answer your other post, pretty much any high flow cat will trigger a cat efficiency code, because they are not as efficient as an OE cat. If the CEL is on, you will fail emissions inspections. It may fail a visual inspection, but I'm not sure. Some people use spark plug anti-foulers to move the rear O2 sensor out of the exhaust and "trick" the engine computer into thinking the high flow cat is OK, but this is technically illegal and it will fail a visual inspection if anybody with a brain looks under the car.

[Garrison]

Update:

Problem is still present despite 3 cans of seafoam thru the tank, 1 can (over time) into the PCV, 3 tanks of fresh fuel, the last of which was 89 instead of 87 (recommendation from a NAPA worker).

Also, had a rear 02-sensor spacer installed but I don't believe it was long enough because the CEL came back on. Does this trick require an ECU reset or is the spacer just not long enough?

Finally, the CEL code for malfunctioning IACV came on, and I happen to have a spare, so I'll just replace it and hope for the best. Are there any special considerations for IACV replacement?

Thanks for any answers

[Garrison]

Replaced IACV and the emissions check says that p0420 code is has not returned, and likewise, the catalytic system checks out alright as well.

We shall see if the driving conditions have improved in the next few days.

[Garrison]

Driving conditions did not improve until yesterday, when a mechanic-friend of mine suggested that the TPS might be to blame. After unplugging it, the CEL came on (obviously), and the idle was high (1500 vs 800), but all symptoms of the lug/chug, dying, surging, etc, are all gone. Replacing the TPS with a new one off of ebay for $25. Will report back with the results.

[Garrison]

Replaced TPS and rotated (just sticking it in there doesn't quite do it) and the problem is gone. No codes, and car drives awesome again. I know not everyone has a voltmeter, so...
For anyone else that might have this problem: stick the TPS into the slot with the spring depressing tongue right up against the throttle shaft; rotate clockwise until the idle drops to 800rpm. The screws should be rear-wards on the top screw, and front-wards on the bottom screw.

It's pretty simple, all in all. Happy to answer any questions, but my problem is solved so I'll be absent in this thread otherwise.