1989 TPI 355, open element air filter, no air, no cats, 2 1/4 headpipes into 2 1/2in to a Magnaflow truck muffler (Basically a really big Glasspack, free flowing).

That is my current intake, exhaust, and emissions setup. Don't know if any of these would contribute, but wanted to throw it out there.

Just looking for opinions, or owners who have had similar rough idle problems and thier specific solutions.

honestly vacuum lines being loose, is your heater/ac module behind the dash all hooked up or does it hiss because that can do it https://www.thirdgen.org/forums/inte...anent-fix.html this is a great write up to fix it though

Vacuum lines are all hooked, and relatively new. I replaced ALL of them when I installed this engine into my truck 4-5 years ago.

As for the hissing heater controls, my S-10 does have the vacuum controls, but it only lets out a hiss when I switch from defrost to heat to dash, etc (you know what I mean). Only hisses when I select a different setting, and stops immediately.

I haven't completely ruled out a vacuum leak, but have replaced all of the intake manifold gaskets, vacuum lines, etc. Vacuum leak was my first thought as well, when I disconnect the line from the plenum that operates the heater, cruise control, etc, it runs the same........

ohhh so this is an s10, what did it have in it before the 355 tpi?

1991 S-10, 4.3 TBI, 5 speed, 4X4, was the stock setup, the only thing that has changed is the addition of the TPI 355. The first TPI engine I had installed was an 87-88 305..... but it was worn out. I found a guy out on the Bangor sub base that wrecked his 1989 IROC, and I bought/pulled the motor and memcal.

I wasn't even aware the engine had been rebuilt until I got the engine home and stuck a pen light next to a spark plug hole and saw 030 stamped into a piston.

Jared

okay so what if anything did you do to the stock fuel delivery system? better flowing pump? cuz i'm suspecting that thats your issue

Holley 255lph pump, which was one of the first mods I made to prepare for my ZZ4 motor, which is not installed as of yet, but is in the garage still wrapped up.1991 Std Cab Short Box 4x4 w/1989 TPI 355 and NV-3500 5 speed - MSD 6A, MSD Blaster Coil, MSD Distributor, Mallory 8mm Slicone Plug Wires, Holley 255lph Fuel Pump, MSD 24lb Injectors, Stealth Performance 4X4 Notched 5qt Oil Pan, JTR 2.8 Motor Mount Setup, Dual Flex-a-lite 210 Pusher fan, 94 Vortec 2 core Radiator, Spectre Air Filter, Magnaflow Exhaust, Sunbird Non Turbo Instrument Cluster with GMC Typhoon Bezel and Brackets, 3 gauge Pillar Pod with Autometer Ultra-Lite Oil, Water, and o2, 2001 S-10 60/40 Split Bench.
"In the Garage" .020 over ZZ4, Edelbrock Hi-Flo TPI lower manifold with runners and ported upper plenum, TPiS 58mm throttle body, BBK Adj FP Regulator, and Brand New in the Factory GM Boxes...... a set of NOS 1989 Magnesium Corvette Valve Covers. Probably won't get around to installing any of this until my current 355 craps out on me.

This is my signature from V8S10.org, it will help to know where my project is ultimately headed (although it will not reveal anything about my current idling issue)

1991 Std Cab Short Box 4x4 w/1989 TPI 355 and NV-3500 5 speed - MSD 6A, MSD Blaster Coil, MSD Distributor, Mallory 8mm Slicone Plug Wires, Holley 255lph Fuel Pump, MSD 24lb Injectors, Stealth Performance 4X4 Notched 5qt Oil Pan, JTR 2.8 Motor Mount Setup, Dual Flex-a-lite 210 Pusher fan, 94 Vortec 2 core Radiator, Spectre Air Filter, Magnaflow Exhaust, Sunbird Non Turbo Instrument Cluster with GMC Typhoon Bezel and Brackets, 3 gauge Pillar Pod with Autometer Ultra-Lite Oil, Water, and o2, 2001 S-10 60/40 Split Bench.
"In the Garage" .020 over ZZ4, Edelbrock Hi-Flo TPI lower manifold with runners and ported upper plenum, TPiS 58mm throttle body, BBK Adj FP Regulator, and Brand New in the Factory GM Boxes...... a set of NOS 1989 Magnesium Corvette Valve Covers. Probably won't get around to installing any of this until my current 355 craps out on me.

could be its getting too much gas and flooding

Fuel pressure is within spec, and I have already replaced the FP regulator.

I am also running 24lb MSD injectors, but that has been programmed into my current PROM.

And my pillar mounted O2 gauge would show if it was running rich...... O2 sensor has been replaced as well......

It bounces between lean and the top end of Stoich, which I understand is what is normal.

hmm, engines been rebuilt, how aggressive is the cam? if you know? could cause it to idle low, other then that i'm out of ideas aside from vacuum leaks

Well, I can't answer that for sure.

What I can tell you is that the truck put down 207hp & 303tq on the dyno...... which is right on track for being a stock, or a remanufactured stock cam.

I am only saying that because of the engines stock HP-TQ ratings -minus- parasitic-drivetrain loss

Do you have a scanner? Could be Coolant temp sensor, throttle pos. sensor, etc.

I am working on getting my APU1 set up for data logging, no luck yet.

CTS is fine, my electric fans are controlled by the computer and are coming on and turning off at the correct temps according to my manual temp gauge.

I adjusted my TPS sensor not to long ago.

I am not trying to shoot down anyones ideas, but am hoping someone comes up with something I haven't thought of or haven't tried.

Keep em coming, thanks guys.....

mine was a charcoal canister purge valve leaking vapors all the time. then a bad egr solenoid not holding vacuum. thats just my recent. for the canister purge a quick test is open the gas cap when running and see if it smooths out even slightly.

Have you checked your egr valve? It may be stuck partially open.

That is something I have considered, a little hard to get to without removing the runners and plenum but it is on my list. Nice to hear from someone that thinks that it could get stuck partially open though, wasn't sure one way or the other......

If it were stuck a little open would the ecm throw a code?

That's a good question. I know the ecm checks for increased temperature at the egr valve when requesting egr by using a temperature probe mounted on the egr. But I doubt if it is being monitored at idle. I wonder if you could somehow check the temp probe with a meter with the car idling. But that means you would also need to know what is a normal reading. What I'm getting at is that if the egr is leaking, then the probe would sense the increased temperature and you should be able to measure that with a meter. Hope that makes sense.