Just wanted share a little info for anyone chasing an off idle stumble on a TBI engine. I have had my 1988 Suburban V10 about two years now and it has always had an off idle stumble, worse when cold. In addition, it would leak oil past the guides when parked and smoke when started, but otherwise ran OK for the high mile heavy truck it is. Knowing I would have to replace the heads at some point I started gathering parts. In the mean time, I replaced the EGR valve thinking that might cure my stumble, it did not.
Finally got some time and tore the top end down to the short block. Bores looked OK and oil pressure has always been good so we left that alone. Replaced the timing chain and gears and water pump with a Stewart Stage II. Put the ATK reman heads in place and started bolting on all my goodies I have been collecting: NOS throttle body and injectors with new IAC and TPS, new AC Delco distributor with cap and rotor, plugs wires etc, new EGR solenoid and MAP sensor, adjustable Fuel pressure regulator and injector spacer kit, new GM fuel pump (surprisingly cheap) and filter, Edelbrock intake manifold, Thorley headers and connecting pipes, Salad bowl,K&N etc. Pretty much everything, except the EGR valve since, you know, that was new anyway, right? Well, she fired up and ran pretty good once we replaced a defective Injector pod, and the stumble was diminished but still there for sure. We readjusted timing, cranked fuel pressure to 14lbs and it was still there. I looked at everything we had done and surmised that the only non oe replacement part we hadn't used was the EGR valve and the temperature control switch. I called the local AC Delco distributor who had these on the shelf and we replaced these two items. In comparing the EGR valves there were some obvious differences that we didn't notice the first time we had replaced it. Probably because the original EGR had already been replaced before we bought the truck.
Well, the good news is that the factory EGR fixed our stumble, not only that but the power gains we expected from the upgraded parts really became noticeble where they were not prior to the valve replacement. I am truly stunned at how much this singular item detracted from the performance of the engine and just wanted to share this with the group in hopes that it might save someone else some aggravation down the road.
Finally got some time and tore the top end down to the short block. Bores looked OK and oil pressure has always been good so we left that alone. Replaced the timing chain and gears and water pump with a Stewart Stage II. Put the ATK reman heads in place and started bolting on all my goodies I have been collecting: NOS throttle body and injectors with new IAC and TPS, new AC Delco distributor with cap and rotor, plugs wires etc, new EGR solenoid and MAP sensor, adjustable Fuel pressure regulator and injector spacer kit, new GM fuel pump (surprisingly cheap) and filter, Edelbrock intake manifold, Thorley headers and connecting pipes, Salad bowl,K&N etc. Pretty much everything, except the EGR valve since, you know, that was new anyway, right? Well, she fired up and ran pretty good once we replaced a defective Injector pod, and the stumble was diminished but still there for sure. We readjusted timing, cranked fuel pressure to 14lbs and it was still there. I looked at everything we had done and surmised that the only non oe replacement part we hadn't used was the EGR valve and the temperature control switch. I called the local AC Delco distributor who had these on the shelf and we replaced these two items. In comparing the EGR valves there were some obvious differences that we didn't notice the first time we had replaced it. Probably because the original EGR had already been replaced before we bought the truck.
Well, the good news is that the factory EGR fixed our stumble, not only that but the power gains we expected from the upgraded parts really became noticeble where they were not prior to the valve replacement. I am truly stunned at how much this singular item detracted from the performance of the engine and just wanted to share this with the group in hopes that it might save someone else some aggravation down the road.
