Need Help

[NEO]

Ok this isn't my car but a friends. We have been trying to fix this for a while now. The car, 89 TTA, he picked up off of ebay about a year ago. The car ran fine when he got it but shortly after it started having problems. When cruising and the motor is at 1500 to 2000 rpm the car will start to buck/surge/miss. Once it starts doing this and it will not quit until it is out of this range.

What is known about the car

TA 49 turbo (15 psi)
009 injectors
New adjustable fuel pressure regulator (set at 42psi)
ATR plug wires
New spark plugs
3" THDP
Test PiPe
ATR cat-back exhaust
ATR dial-a-boost
Reds 93 chip
Walbro fuel pump
new egr valve
62mm throttle body
throttle body coolant bypass

Tps is at .42 idle 4.56 at wot. What we have tried is swapping stuff out of my 87 T and seeing if it goes away. So far we have swapped out the following:

Computer
Chip from another buddy with 009's
Coil Pack with Module
MAF
Throttle position sensor
ESC module

Nothing made a difference.

When he replaced the throttle body these symptoms seemed to go away but are now back. The car is now starting to "hunt" for an idle. BLM's in gear about 128 in park and 140 in gear sitting still.

Fuel pressure goes up 1:1 when getting into boost and fuel pressure stays when you shut the car off.

What could be causing this? We were thinking IAC, or O2 sensor.

Thanks in advance,

 

[SlowTTA]

I would go with your first assumption, the IAC. Seems to be the next logical step. While reading the problem it sure smelled like a bad MAF. Mine did the same thing, ironically, right after I purchased my car...hmmmm

 

[NEO]

No, we tried my oem MAF, that had no problems when I took it off my car to switch to the translator, and it ran the same. Also, we tried the tap test on the MAF and it didn't effect the way the car ran.

Ignore the BLM's numbers posted, I confused some numbers. The IAC count in park was at 28 and in gear, sitting still it was around 40. I will get BLM's later today.

Thing is, when we picked this car up, the guy he bought the car said he had programmed some chips for the car because he was having some problems with the idle. He also had just replaced the EGR valve, he said he believed this was part of the idle problem and that it was now fixed so he put reds chip back in it.

We set the idle and tps from the instructions on the gnttype.org. When the setting the idle noticed that the idle screw was so far out there was washers behind the spring in order to keep enough pressure on the spring to keep the screw from moving.

Today we are going to try blocking off the egr to see if it improves before trying to find the problem in that circuit, and then we will try the IAC motor.

Thanks,

 

[2QUIK6]

Yes, I think the next logical step would be to eliminate the EGR from being the problem. If its stuck open that could effect idle, otherwise it should be closed at idle. Maybe its fluctuating at cruise at 1500-2000 rpms is why its surging....block it off and see if the surging goes away.
Remember though, the EGR allows you to run higher timing at cruise, so don't leave it blocked off for extended amount of driving, you may start getting spark knock at cruise unless you reduce some cruise throttle timing.