Grumpy5.3

iTrader: (14)

do you have a leaky intake gasket?????

chevygirl

iTrader: (69)

He says he has checked all the ground wires and fixed anything he found that didn't look right. The intake was just put back on with this new engine and also on the last engine with the same rough idle. The intake was replaced with a factory one 2 trips ago to the dealer. What I don't get is how the idle will be off a little and then it will get worse. It was doing this with the old intake too. Maybe it is worse with the new one but it is hard to tell. Sometimes it sounds okay for a little bit and then it starts messing up. He thought he had it fixed so I picked it up because he has so much work in the shop there is no room for it. I have to wait until he can get room to take it back. He really doesn't know. My father and I have been over everything a hundred times and can't find anything. We just started swapping parts and still haven't fixed it. It is like it has to completely break down before they will fix it. It acts like it is surging at idle sometimes. When you start it is sounds like it is missing and the truck shakes. We can't hear any vacuum leaks anywhere and everything has been replaced.

Yelo

Get an EGT gauge and see what your exhaust temps are running....I'm betting you're running VERY rich (low EGT's = rich A/F). also, a bad distributor or ignition module will cause ALL of the problems your describing (especially the intemittant periods of running fine).

chevygirl

iTrader: (69)

What does the egt stand for? Where could I get something like that? I have a new distributor and module (replaced twice) about one year ago. I will see what I can find out about the exhaust temps?

SS_bnoon_SS

iTrader: (3)

EGT= Exhaust Gas Temperature.

SS_bnoon_SS

iTrader: (3)

Also, just on a hunch... what does your coolant temp run at?

Reason I ask is that I had a friend put a lower temp thermostat in his TBI truck without reprogramming the ECU. When it was cool outside, it ran fine, but when it was hotter out it ran kinda like you're describing because the ECU forced the truck to run rich as it was trying to get the coolant up to normal operating temps... but couldn't, because of the lower temp t-stat.

chevygirl

iTrader: (69)

I don't know what the coolant sensor is running out. We checked it ourselves with the multimeter to test resistance and we replaced it twice. The guy said he checked it too and it was right. Everything is GM and oem. I am using the factory gm thermostat. I will mention it to him again. He said he checked it with the tech tool and it would not pick up a lean or rich mixture but that was a year ago he checked that. If it does the weird idle when it is cold also does that mean it is running too rich in the beginning and after it warms up? I don't seem to be getting bad gas mileage? Do you have to wire up one of those gauges or do they make something that you can read at the tailpipe?

Yelo

Let's try this a simpler way: What HAVEN'T you changed ??...What parts are still stock??

The coolant temp things sounds plausible too....what temp thermostat do you have ??

Also....have you changed the fuel-filter since this started happening ??

Grumpy5.3

iTrader: (14)

I have seen one doing that and the o2 sensor was the cause. I found it by getting thetruck to act up and actually ground out the o2 sensor wire.
just a thought!!!

Bowtie70SS

iTrader: (10)

My dad's 91 had a bad coil. It arced out the bottom of the coil and to the intake...his truck had like 170k on it when it did that. I liked to never figured it out because it would spark fine...sometimes. A coil is cheap, also pay someone with a scanner to drive around with you and watch what the truck is doing.

Dave