Hi, I'm trying to get this damn thing running right! It's a 91 TA GTA l98 5.7 tpi 76k mi. My brother brought it to me with a rolling idle with what seems to be a miss also. Under acceleration it is running rough and wont go past 1/2 throttle with out bogging down. Put on fuel press guage 36psi at idle, about 41 when opening throttle ?ok? It was time for a tune up so we did plugs, wires and new ign module. Cap and rotor looked good. No change. Only odd thing I noticed was the plugs in the right bank (2,4,6,8) appeared black ie running richer on that bank if possible?Not oil fouled. Idle is going from 750 to 950 and the timing is jumping from 15 deg to 25 deg while idleing. No trouble codes set. No knock signal present. Checked for vac leaks none found. Messing with it last nite I used an angle screwdriver and got under the egr valve and pushed up on the diaphram. The idle smoothed out, timing at 15 to 16 deg stable, smoothed out the miss, but the o2 reading went to .8 and stayed rich. Good throttle response???? I give what the ^%&^ is going on with this thing??? thanks Mark P.S. Car is all stock

 

get a scantool and see if the coolant temp sensor checks ok(ohm readings listyed in GM manual if u have a meter) and check the fuel regulator to see if it has a pinhole and letting fuel into the engine
later
Jeremy

 

That fuel pressure sounds a bit low for a TPI too, should be set for 43 with vacuum line to regulator pulled and plugged.

 

Thanks jeremy, The cts was showing 80c. The regulator sounds like a great idea i'll check that tonight. Every other egr valve I have lifted off its seat before at idle has caused rough running and a stall. This one started running better? I also noticed there is only one o2 sensor on the driver side exhaust manifold. Seems to me it should be after they come together or one on each side?How will the computer know if there is a problem on the 2,4,6,8 head? Vern I'll check the fuel pressure how you described and post the results. thanks Mark

 

vern, fuel pressure with key on eng off 40psi. No leak down. eng idle vac line pluged 44psi. eng idle vac on reg 35 psi. Still can't figure out why when egr is introduced engine smoothens out?

 

do you have the plug wires routed so they don't touch the manifold, cause that sumbitch can get hot and cause problems with the electrical impulse in the wire if they are touching.

 

no wires touching nick, Est signal (timing) and idle moving up and down together in unison. open egr and it smoothes out?

 

replace your egr valve

 

You say that your right bank is running rich.
In my 91Z28 my one bank was running very rich and found one injector was bad. Replaced it and ran good only to find out 2 months later another 3 injectors were also bad . Had all 8 replaced and ran great.
If you have one bad injector you can have all 4 on the one bank spray too much fuel since all 4 spray at the same time and are connected.
Do a resistance test to check all injectors. If the are grey (Rochestor) chances they have gone bad.

 

If you can, read the part number stamped on the top of the EGR Valve. It should end with the letter "N." This stands for a Negative Backpressure EGR Valve. If it's a "P" or just the part number without a letter, it's the wrong type. "P" stands for Positive Backpressure EGR Valve. And one without a letter is a Port EGR Valve.

The EGR system should not be "On" while idling.

Sorry, I just read your PM. Did not mean to "Blow you Off"

Bill