99 Imp 2.5RS Idle issues

[torxxx]

Hey guys, did a timing belt/water pump/reseal/clutch/rack and pin last night at my buddies shop. Got everything put back in and as we were running it in to burp the cooling system we noticed the idle surges and has a random cyl misfire.

 

2.5L SOHC, 5MT.

 

No CEL as of yet. We didnt take it out for a test drive because I wanted to go through and make sure everything was hooked back up. I've done tons of these SOHC 2.5s and have not had this issue.

 

Idle surges between 400-1000 rpms and appears to get worse the longer we let it run. Unplugged the MAF sensor to trip a code and make sure the system was picking up faults and it seems to be working fine.

 

Replaced the vac line from the intake to the cruise control motor, but other than that we didnt mess with anything else. Intake stayed on the engine, timing marks were all @ 12 oclock (I put the belt on myself, double checked my marks and had the shop owner check the marks as well.

 

As I was falling asleep last night I thought about the airbox setup, and I'm almost thinking I may have ripped the rubber throttle body coupler away from the airbox on the bottom. Its the only part that I couldnt visually inspect last night.

 

Gonna head back down to the shop and go through the motions again, i'm sure its going to be something silly thats causing it (had 3 sets of hands helping, which tends to lead to something left unplugged or unhooked)

 

Any/All ideas are appreciated.. btw I carb clean tested the intake/vac lines. No vac leak I could find

[Fairtax4me]

Could be a bad intake gasket or fuel injector o-ring if the airbox isn't the problem.

Might try cleaning the IAC valve, or replace it with the one from the old engine.

[torxxx]

Cleaned off the block, its a 2.0 bottom end with 2.5 heads. Problem isnt all time time. Comes and.goes. acrually made the car stall just now. Intake gasketnleak would cause problems all the time wouldnt it? We are gonna go clean the iac when we get back to the shop.

 

Car runs awesome as long as its not idleing. Has full power. Temps are negative 15F, would fuel line icing cause the problem to come and.go?

[torxxx]

ok, it finally popped codes. 1510 1512 1514 1516

 

I know the 1507 is the neutral safety switch issue with the 5mt's. I've only seen that code come on the DOHC 2.5, not the SOHC 2.5

 

We cleaned the IAC out, didnt seem to change anything. I'm not real familar with the newer IAC's, I'm used to the 2.2L IAC that has the rotor/vein setup. This newer style uses a plunger style correct?

[Fairtax4me]

Yeah that one should have the black plunger type with the round housing.

Those have some issues and you can take them apart to clean but I think you might have a wire issue to the sensor or the sensor is damaged internally.

Those are all low input codes which could mean there isn't enough voltage getting to the sensor, or there is unwanted resistance between the ECU and sensor.

 

If you got a P1507 as well check the wiring to the neutral position switch, and make sure the switch isn't sticking when you shift in/out of neutral.

[torxxx]

I'll check the NSS tommorow if its still acting up. We changed out IAC, cleaned up all the grounds, cleaned the throttle body and MAF, adjusted the tps to .477v and it seemed to make a difference. No more codes, runs smoother but still has a slightly bouncing idle.

 

I cant remember which sensor is the nss on the trans. Brown connector or Gray connector?

[Fairtax4me]

Brown. It's the rearmost sensor.

[torxxx]

kk thx for the info!