What could cause jerking off the line and when the gas pedal is released from speed? Overall not a smooth ride. Gets about 450km/Tank.

Edit: is there any info on IACV trouble shooting?

 

Your post is kinda vague. Automatic or manual transmission? Start simple, check the mounts and bushings.

As for the IACV, it's best to just remove it and inspect it. Clean it if it's dirty. Might also want to clean the throttle body while you're at it.


Has the MIL (check engine light) come on or flashed?

 

No MIL or codes stored. I have scanned it with no result.
ECU appears to be functional and communicating well with the scanner.
Motor mounts/bushings are all good. intake + manifold removed, cleaned, re-installed with new gaskets. Idle can be anywhere from 400 rpm nearly stalling to 1500 rpm and bouncing. It has never completely stalled on me.

 

How often does the idle fluctuate? Constant up-and-down, or just sporadically?

Have you tried resetting the ECU and doing the Idle Relearn?

It might be time to replace the IACV or the throttle body. How many miles are on the car?

Have you checked for vacuum leaks?

PCV is okay?

 

Idle will be stable until you touch the gas pedal at which point it will hunt until the ECU 'takes charge' and places it at 750 rpm. Interestingly a touch of the gas pedal will make the car rise normally, fall to 800~ rpm then it will climb to 1300 and hunt around before settling at 750 again. If you are giving it gas while driving it seems totally normal. Only stumbles or jerks when coasting no gas or right off the line.

I have replaced IACV, PCV, intake manifold and TB gaskets, TPS sensor ( + calibrated it), MAP, front/rear O2 sensors, Coolant Temp Sensor, Spark plugs, Timing Belt (+ h20 pump).... basically run out of ideas.
Definitely no vacuum leaks.

I have reset the ECU by pulling the "backup" fuse and removing the neg battery terminal. Is there a procedure to relearn idle besides allow it to idle with no accessories on for 10 min?

Car has 135,000 km (~85,000 miles?)

 

All that and it's still acting funky? Hmm.. I'm at a loss, my friend. Have you tried swapping ECU's? I know it's a long shot, but, damn, you've already gone this far with it.

- Turn off everything electrical. Lights, heater/ac, wipers, radio, rear defogger, etc.
- Start the car and hold it at 3,000 RPM until the radiator fan comes on.
- Let the car idle for five minutes. (if the radiator fan comes on, don't include the time that it's running in the five minutes)


Just a quick note: You want to remove fuse #6 to reset the ECU, not fuse #9.

 

I'll re-try the idle relearn and hope for the best.

Ya I'm at a loss as well... Would take it to a pro but I feel like they would just give me a run around with this ridiculous problem...

 

Update!:

Hooked up the OBD2 scanner last night and found no trouble codes. ECU appeared to be totally normal with no communication issues or anything terribly out of whack.

All sensors seemed to be trouble free. ECU was re-flashed with some result, idle quality seems to have improved yet is still unstable. Stumble and jerk on accel/decel seems to have improved somewhat.

Only thing I saw to be unusual was that the indicated spark advance on the scanner was 25 degrees. Is there a way I can ensure timing is appropriate without removing timing covers. I have not ever attempted to time a non-distributed engine.

 

How tight it your throttle cable? Make sure it goes slack and tighten it there. I had the problem where when I was at a low speed I would try to ease in or ease off the throttle and it would jerk.

 

My es1 had the same problem a the culprit was a bad fuel pump.

 

More specifics on the symptoms from bad fuel pump?