OK...Here we go again mechanics.

[BolilloLoco]

Clogged catalytic converter?
Weak fuel pump?
Faulty fuel pressure regulator?
But most likely a vacuum leak somewhere.

[HDWRENCH]

A temp sensor cause a rough idle?

yes in many cases the sensor is not an " open " so on older vehicles it does not know to set a code a temp sensor can think its -30 or + 250 and it adjust based on incorrect info

[rtarcher]

I think that model still has egr valve. Check and see if its stuck .

In my 93 Blazer with the 4.3, I used to have to clean chunks of carbon out of the EGR fairly often starting in about 1999. The first time I did it, it took about 2 hours. The last time I had to clean it out, it took about 15 minutes. I had just the right bend in a long flathead screwdriver and the perfect swivel combination for my socket set

Todd

[banzai]

I just drove it for a few miles. Runs like a scalded dog until you come to a stop. It is better though.

That sounds like a vacuum leak to me. When rpm is high, any vacuum leak air will be a smaller percentage of the total, so it won't be noticeable, if at all.

What did you use for spray when you were searching for leaks?

Try restricting the intake air flow down to almost nothing using some cardboard or an old shirt (big stuff so nothing can get sucked into the intake). Try different amounts of blockage, trying to find one where the idle will be smooth and about the correct speed.

If the truck will idle well with a heavily restricted intake, then you know you have an un-metered secondary source of air getting sucked into your intake.

[Dale Moser]

Have you done the full seafoam treatment? Suck it in the brake booster vacuum hose and all that?

Sounds like a sensor to me.

Have a code reader plugged in at auto supply?

[Goldeneagle]

That sounds like a vacuum leak to me. When rpm is high, any vacuum leak air will be a smaller percentage of the total, so it won't be noticeable, if at all.

What did you use for spray when you were searching for leaks?

Try restricting the intake air flow down to almost nothing using some cardboard or an old shirt (big stuff so nothing can get sucked into the intake). Try different amounts of blockage, trying to find one where the idle will be smooth and about the correct speed.

If the truck will idle well with a heavily restricted intake, then you know you have an un-metered secondary source of air getting sucked into your intake.

I'm leaning towards a vacuum leak. I think I just haven't found it. I sprayed with WD-40 but I'm going to get some spray carb cleaner and try again.

Have you done the full seafoam treatment? Suck it in the brake booster vacuum hose and all that?

Sounds like a sensor to me.

Have a code reader plugged in at auto supply?

I have a code reader, but it is OBII. They didn't start OBII until 1996. The check engine light is NOT on so I don't think it is throwing a code anyway.

[banzai]

I'm leaning towards a vacuum leak. I think I just haven't found it. I sprayed with WD-40 but I'm going to get some spray carb cleaner and try again.

Try restricting the idle to confirm that the you have an air leak. If you can make it idle well by partially choking off the main air supply, you will be in much better position to solve this.

Besides a vacuum leak, another problem that can cause similar symptoms is a bad Idle Air Control valve. If it is stuck open a little, your idle fuel mixture will be too lean but higher rpm will run fine.

[Bullfrog90]

spider injectors

My son has a 97 with the 5.7 and was doing the same thing as you described and it was the spider injectors.

[Goldeneagle]

Try restricting the idle to confirm that the you have an air leak. If you can make it idle well by partially choking off the main air supply, you will be in much better position to solve this.

Besides a vacuum leak, another problem that can cause similar symptoms is a bad Idle Air Control valve. If it is stuck open a little, your idle fuel mixture will be too lean but higher rpm will run fine.

I'll try choking it down tomorrow. I replaced the IAC today with no change.

[TxDispatcher]

Is siphoning it out not an option? I'd rather try a very small amount of bad gas after siphoning out all I could, than 15 gallons

I have no way to catch 15 gallons of gas.

Didn't think about that

And if things can't get worse, I just lost my balance leaning over the engine. I busted the connector to the IAC.

Hope you're okay although a pain in the butt, the connector can be fixed cheaper than you can be careful!

[Airtech]

Ck back on the connector on the IAC motor. You mentioned that you broke it. If any of the wires are broken or out of position, the new IAC would not function properly. Also this vehicle has a MAP sensor that could cause problems. May be time to get to someone with a full blown scanner and the knowledge to use it. All this guessing is costing you more than a scan reading. Look close at those wires at the IAC connector, one may be broke inside the insulation.

[Goldeneagle]

Didn't think about that



Hope you're okay although a pain in the butt, the connector can be fixed cheaper than you can be careful!

I wouldn't know what to do if I wasn't bleeding.

Ck back on the connector on the IAC motor. You mentioned that you broke it. If any of the wires are broken or out of position, the new IAC would not function properly. Also this vehicle has a MAP sensor that could cause problems. May be time to get to someone with a full blown scanner and the knowledge to use it. All this guessing is costing you more than a scan reading. Look close at those wires at the IAC connector, one may be broke inside the insulation.

I really haven't put that much $ into it yet. Just normal tune up parts that it was about time for anyway. The only unplanned part has been the IAC. I would have thought that as all of the sudden the problem came on that I would fine a vacuum line off somewhere. But there is not. I got a new connector for the IAC. Will wire it in today. I wish I had the $ to just take it in somewhere, but I don't at this time. I'll get it sooner or later.

[Lightning48]

Have you ever ran a bottle of Seafoam thru the vacuum line?? Get engine to operating temp,with engine running pull vacuum line at brake booster,cover half of the check vavle and slowly pour Seafoam in until engine just starts to stutter,pour the whole can in,when can is empty kill the truck and let sit 10 min. then start and go drive. This will remove carbon build up on top of valves..

[JMR]

Did you ever check fuel pressure? Just cause it runs, doesn’t mean you’re getting adequate fuel. I had one doing the same thing, run around all day until you tried to take off. Loading on the trailer was nearly impossible. Always check fuel issues first then fire.

[tpepper70]

Check the injector spray while it's running. If it is dribbling, not a nice spray, then its dumping too much fuel and loading the engine up at idle, but clears when you rev the engine up due to air flow. What was wrong with mine when I had this problem. Bought new injectors and problem cleared. Good luck.