keznevin

I have a 1988 c1500 with a 5.7 tbi. When I first start the truck in the morning it has an awful miss and its fighting back and forth trying to find an idle. It idles up then down and back and forth till it warms up then once the truck warms up and gets to running temp the miss goes away and the truck runs like a champ. Any info will be greatly appreciated. Truck has new distributor, plugs, and wires. I search on here before I posted but can't find any post with this problem.

ZONES89RS

iTrader: (25)

Welcome to LS1Tech.

Have you tried cleaning up the throttle body? Have you tired running sea foam thru the intake?

keznevin

Thanks for the welcome. No i haven't either one of those. Do you recomend this? I've taken the tbi off before i can do that and clean it this weekend.

ZONES89RS

iTrader: (25)

No need to clean the intake like that, you can but you just need to spray a can of carb cleaner in it while it is not running and i use a old tooth brush to take care of scrubbing detail.

Then for the sea foam, while it is running, slowly pour a small steady stream into the TB on both sides going back and forth but not enough to let it die. Keep doing it till it is an empty can. You might have to keep it running with one hand while you pour with the other.

Once it is empty, let it run and free rev the engine a bit and it will probably smoke like something is seriously wrong, it is just all the carbon being removed, no biggie.

The take it for a test drive and let us know if it is any better.

Z

pancherj

Are the engine and computer stock (no mods at all)? It sounds like your IAC is hunting to keep idle. It may be doing this for several reasons (fuel pressure bouncing around, throttle plate too far open at idle, etc.). The fact that it goes away after the engine is warm is odd. Maybe the intake or TBI gasket isn't sealing perfect when the engine is cold?

cambirdracing

iTrader: (4)

I wouldlook at the hose that goes from the pcv to the tb. Those will clog up and create this problem also. Along with the bottom of the tb.

keznevin

the motor was rebuilt about 15000 miles ago and all i done was bore it 30 over to clean up the cylinder walls. otherwise basic rebuild. The thing that makes it hard to diagnose is that it only does this for about 2-3 minutes then it runs great.

alamantia

iTrader: (10)

I had a similar problem with a 1988 S-10 2.8, sometimes when I cold started it in cold temps it would fire right up but stumble around searching for idle, then it owuld shoot up to around 2000RPM and stay there. The only way I could get it to come down was to shut it off and restart it. Problem is it would only do it sometimes and of those sometimes only when it was ice cold. I tried replacing the temp sensor for the ECM, the one in teh intake manafold. That didnt fix it. I tried pulling out the IAC and cleaning it. I even installed a new IAC. That didnt fix it. I put a new EGR on it. That didnt fix it. I put a throttle position sensor on it and it went away long enough for me to sell it. I dont know if it ever came back after that. TB gaskets rot on this things all the time, that was my next investment. Thing is I figured it would hapen all the time if it was a vaccume leak.

rescuegunner

I had same issue on a '92 305 TBI Camaro. I ended up taking the IAC motor off completely and cleaning the idle port out VERY thoroughly with carb cleaner. There was what seemed like 10 pounds of carbon built up in there. After convincing the embedded, hard crusty carbon out of the port (had to use screwdriver to break up the bad stuff) I put the idle air control motor back on. Worked like a charm after that.

wickedbluess

iTrader: (20)

What is the iac and where is it located.
Thanks raul

EDS01SS

iTrader: (30)

Sounds alot like either a intake air temp sensor problem or a coolant temp sensor problem to me.Pull your plugs and check them to see if the engine has been running rich.If either of those sensors are the problem then the computer is going to dump fuel into them cylinders due to incorrect temp readings.