So I recently swapped a 5.7 TPI engine into my 'bird that originally had a TBI 305. The wiring harness was in good shape, the engine was supposedly recently rebuilt, and looks like it too. When I firing it up for the first time it ran really rough and through a code 34 for the MAF. The MAF circuit checked out fine and I discovered the sensing wire was broken so I got a new one. It runs better but still rough and wants to die at idle, when you give it gas it just seems to get even rougher. I did notice that if I block the MAF partially with my hand it clears up and runs smoother. Anyone have any idea?

 

Have ALL vacuum and intake leaks been eliminated? Don't overlook the EGR and brake booster, and verify that the PCV is getting its air from the TB fitting and not from a breather cap.

Does this happen even after it is a full temperature and in closed-loop?

What calibration was used?

 

It does it when cold and warm, haven't run it very long since in was put in yet. Haven't ruled out vacuum leaks yet, but I can't hear any big ones. I thought maybe the hand over maf was indicative of a vacuum leak. I planned on squirting brake clean around my intake tonight and cleaning the IAC valve out. It's at like over 100 counts when idling/running rough. Any way to check egr
operation without taking the intake apart? I don't think it went closed loop yet, didn't run it enough to get O2 up yet. Plus I have headers. Not sure on calibration.

 

Also, a few questions. Typical IAC counts should be around 15 at idle, right? What are typical MAF and air flow readings at idle?

 

Hey I have a 88 gta with the 5.7 350 tpi here's my problems

Takes a long time to fire up I researched a bit about it and was told its call long crank syndrome ... Also under heavy load my car bogs down at 2500 - 3000 rpm but at idle it runs great ...

Here's the parts I've replaced
Fuel filter OEM
Fuel pump OEM
Wires 8mm
Plugs OEM
Air filter ( k&n )
Tps ( delco OEM)
I have no idea how to check for a vacuum leak or which lines are the vacuum lines , I was really thinking its my fuel injectors , would I be right ?? I do sometimes get a strong gasoline smell when I start it sO would it be leaky injectors ??

 

Hey I have a 88 gta with the 5.7 350 tpi here's my problems

Takes a long time to fire up I researched a bit about it and was told its call long crank syndrome ... Also under heavy load my car bogs down at 2500 - 3000 rpm but at idle it runs great ...

Here's the parts I've replaced
Fuel filter OEM
Fuel pump OEM
Wires 8mm
Plugs OEM
Air filter ( k&n )
Tps ( delco OEM)
I have no idea how to check for a vacuum leak or which lines are the vacuum lines , I was really thinking its my fuel injectors , would I be right ?? I do sometimes get a strong gasoline smell when I start it sO would it be leaky injectors ??

 

Okay, update time.
Car runs much better with MAF unplugged, still could run better but I assume that's to be expected with it running on backup spark and fuel. With the MAF unplugged the "MAF" reading stays steady at around 10 gm/sec at idle but the calculated airflow is at like 215 or something high like that. Wit it plugged in they are close to each other but the reading jumps around from 5 - 11, although the car does run so bad with it unplugged that I need to give it part throttle to keep it from dying. Checked grounds at the ECM, they appear to be good. IAC is a bit high but the throttle blades are a bit dirty and haven't cleaned the IAC passages yet. It does fluctuate and get down to about 50 counts with the MAF unplugged. If the engine runs just about fine with the MAF unplugged can I rule out mechanical issues?

 

FINAL UPDATE!
After checking ECM grounds, MAF grounds, MAF power relays, wiring, Vacuum leaks, engine mechanical, EGR operation, IAC operation, and fuel pressure I felt defeated. I decided to go back to the basics and scope the output of the MAF sensor on my Vantage and what do ya know, it was faulty. "Brand new" Bosch reman from O'reillys. The output at idle was sort of erratic and very noisy. It would oscillate between .5 and 2 volts at a couple Hz. This also explains why my Inj PW was fluctuating rapidly between 1.1 and 3.0 ms.