Don't know what to try next

[rico47635]

Hi. Out of desperation, I have decided to join a forum like this one to see if I can fix my truck. Back in September I bought a 1988 K1500 with a near new 5.7 liter engine (installed in Feb. '10). The truck ran fairly well, but it had a problem with a very low idle when in gear. My mechanic checked it out and said the idle could only be raised with a computer, which he did. The truck ran better for a couple of days then suddenly developed a miss only noticeable when idling.

I have been a Ford man for the last 20 years, so I know very little about Chevy products and what makes them tick. So far my son and I have fixed a vacuum leak it had, checked the fuel filter, and checked the distributor cap. The vacuum leak was slight and it was coming from where the tube that goes to the brake booster is connected to the intake. The fuel filter is fine and the distributor cap looks like brand new on the inside. I don't know what else to check. I thought that maybe the problem could be the IAC, but that wouldn't make the truck miss so much.

The crazy thing about it is that the truck runs down the road just fine--plenty of power, decent gas mileage, awesome acceleration. What could be causing this miss at idle? It's to the point that I cannot drive the truck anymore because it starts missing so bad when I stop that it shuts off. I refuse to fight with a vehicle to keep it running while I am using it.

To be honest, I am so fed up with the problem that I found myself wanting to take a baseball to it and let the junk yard come get what's left after I get done. It's a good thing that I am in my 40s and have mellowed out quite a bit. That's exactly what I would have done twenty years ago after months of trying to figure out what was wrong with a vehicle. Any help would be appreciated.

BTW, the truck got all new wires and plugs when the crate engine was installed in it. I've also had to replace the alternator, two actuators for the heating system, and fix a problem with the wiring in the tail lights. You can understand my frustration with this truck. For only having it four months, it has been troublesome.

 

[rico47635]

I forgot to mention that we tried getting the codes out of the computer. My son said it's repeating code 12 over and over and over again.

 

[badazzbulldog]

bad distributer my 88 3500 i had would do that

 

[Swims350]

have the module in the dist. checked or buy one, egr valve code be the problem also.

code 12 is the all clear code. it does that if there is no code. it is also no signal from esc to the dist I think, which is what happens when it's not running of course.

 

[rico47635]

A bad distributor? Wouldn't a bad distributor affect how the truck runs at normal speed? I can drive this thing 75mph all day long with no problem at all. It accelerates very well too.

 

[rico47635]

Wow. Just checked at Advance Auto. A distributor ain't cheap. The module is less than $100 though. It seems strange to me that it would be bad and the vehicle still run though. Again, I haven't had much experience with Chevys. On a Ford, the ignition module either works or it doesn't, meaning you either have fire or you don't. Unless someone suggests something else, I will see if the local Advance Auto can check this module out.

 

[Swims350]

ppl told me the module can go bad or something, mine had about the same problem. I had a miss at idle but I had an exhaust valve too tight. I found it out by it sucking my hand on the tailpipe since I had duals I knew what side. I had to put a new dist. in mine, but not because of that miss, and they had kept telling me it could be bad. Even if it was new could be bad. I had always heard though too that egr or something else would cause it to try and die when coming to a stop.

FYI the idle can be raised, and not by the computer, the computer already knows the idle should be around 800 in park or neutral and 600 in gear. Messing with the computer aint gonna do a thing, it would have to be burnt into the chip.

They say you should not mess with the idle speed screw because it could cause other issues, or the idle being low is being caused by something else and would not fix the problem. The idle screw is covered by a cap on the tbi and has to be drilled out to get to it.

Have you checked your IAC? cleaned it off or cleaned out it's port? it could be screwed up or dirty.

If it's a replacement egr valve it could be casuing problems too. I heeard that unless it's a delphi or ac delco egr it won't work right and the numbers have to match.

check with skip white or whiteperformance on ebay they have them for around $65 or so complete and a warranty. I paid over $110 from autozone for mine and it did not come with a rotor or cap. I think the one on ebay does come with both.

 

[rico47635]

Just got off the phone with Advance Auto. Very helpful people. The fella I talked to said that they can test the module and that it's possible for it to have a problem and the truck still run. I sure hope that it isn't the distributor needing to be replaced. My son and I can do the install, but it would still cost plenty. I tell ya, all this computerized gadgetry was supposed to make cars and truck better, but I sure miss the simplicity of carbs and points!

I would think that if the problem were an exhaust valve being too tight that it would have been missing from the time the engine was put in. The problem with the miss didn't start until a couple days after my mechanic said he adjusted the idle through the computer.

I am also going to check the IAC and spray some cleaner into where it mounts. My understanding is that the way to check it is pretty simple. Just take it out and turn the key on. The plunger should move. If not, it's bad. At least that part isn't too expensive-$40.

 

[Swims350]

I think you are right on checking it.

and yes it would miss from the start with a tight valve, mine did. I was just talking about mine and how they kept saying it was the mod and such.

Yea they check it for free so it can't hurt to let them check it out for you to make sure before you start throwing money at it.

I would also agree and is why I like old school carb setups, they are simple and easy and usually cheap. efi is not.


As for the idle I could be wrong but for the early trucks only thing that can be done is by nurning a chip, idle, timing, removing things like egr and such so the CEL doesn't come on, etc. I don't think you can go in and change things with a computer without burning a chip but I could be wrong.

You can check the egr too, with the engine running, reach under it and lift the plugner thing inside and see if it changed the idle. You can also check it with a vac. gauge/hand pump to see if it holds vac. I heard if they stick it will cause a bad idle. it's only supposed to open once it's warmed up to operatng temps and such. Mine turned out to be bad, would not hold vac.

 

[badazzbulldog]

my issue with the dist was a worn shaft it would wobble at low rpms i was just throwin that out there from my issue i had. you should be able to get one thru a salvage yard if you have too for around 40 bucks