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1988 Chevy Silverado Intermittent rought idle

Tiny
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First, double check the EGR. It sounds like it is stuck (not closing). As far as the wiring, make sure there is continunity through the wire. Many times they break inside and you can't see it.
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Wednesday, October 13th, 2010 AT 10:44 AM
Tiny
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So I hooked up the egr and it was running rough, so I unhooked it, and put a screw in the end that was connected to the erg. I started the truck and it ran better but still rough. I could smell gas. Then my service engine soon light came on. I shut the truck off and ran the diagnostic and got code 32 and 45. I have never gotten a 45 before, even with and the rough idle and the back firing. I turned the truck back on and the code has not come on in the last day.

What do you think this means?
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Thursday, October 14th, 2010 AT 3:03 PM
Tiny
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The code 45 indicates a rich mixture caused by the EGR being disconnected. An open vacuum hose will cause the idle to run rough, that is why it ran better when you plugged the hose.

I hate to say it but I think you need to recheck for the basics such as a vacuum leak.
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Thursday, October 14th, 2010 AT 6:29 PM
Tiny
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Well I got a vacuum tester today and tested the
egr and the engines vacuum pressure. The engine ran a steady 20 in. Of Hg with no bouncing or fluctuations. I put the test on the egr and tried to put 10 in. Of Hg, and the egr would not hold 1 in. Of Hg. I put the test on the egr solenoid and when the engine is reved up the pressure jumps to like 20 in of Hg. I was hard to tell because the dial was 4 ft from me on this test. From this information I feel as though I don't have a vacuum leak and my egr is bad.

Is that what you see from my tests.

I tested the power wire from the connector to the switch and there is no break in the wire. I test the connector that comes from the truck and connects to the door wire harness. And the truck side has no power. The break must be farther in the truck or closer to the source of power. Do you know were the window gets it power from or where that power cable originates?

Thanks
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Friday, October 15th, 2010 AT 3:55 PM
Tiny
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The EGR sounds like it is shot. It should hold pressure. As far as the electrical, follow the power to the fuse box. Have you checked to make sure there is power to the fuse?
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Friday, October 15th, 2010 AT 9:47 PM
Tiny
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Well I got the power windows working there was a wire that got pinched. Thanks for the help.

I put the new EGR in today. It started out running rough, then as the truck warmed to operation temperature it ran smoother. I drove it around town to test drive it. At some stop lights the engine would surge then return to idle, or would stutter and the idle would dip then return to idle. Over all it runs better and I have better and smoother acceleration. When it is Idling though it is still rough with the stumbling and occasional surging.

I don't know what to think now.
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Monday, October 18th, 2010 AT 4:31 PM
Tiny
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We are getting there. The next thing to check (if I haven't already mentioned it) is the idle air control motor. Basically, it keeps the idle steady by allowing air into the throttle body when the throttle plate closes. It is located on the throttle body. Here is a picture of it:


http://www.2carpros.com/forum/automotive_pictures/249084_5_87.jpg



Now, two things can go bad with it. The valve can stick not allowing proper air flow, or it can short internally. Here are the directions I was able to dig up for checking it:

Disengage the IAC electrical connector.
Using an ohmmeter, measure the resistance between IAC terminals A and B. Next measure the resistance between terminals C and D.
Verify that the resistance between both sets of IAC terminals is 20-80 ohms. If the resistance is not as specified, the IAC may be faulty.
Measure the resistance between IAC terminals B and C. Next measure the resistance between terminals A and D.
Verify that the resistance between both sets of IAC terminals is infinite. If the resistance is not infinite, the IAC may be faulty.
Also, with a small mirror, inspect IAC air inlet passage and pintle for debris. Clean as necessary, as this can cause IAC malfunction.

Here is the wiring schematic for the IAC so you can see what wires to test:


http://www.2carpros.com/forum/automotive_pictures/249084_6_14.jpg



The images and information I provided are for 1988 to 1998. Let me know what you find. Chances are the IAC is good (electrically) but there is something causing the pintle to stick.

I'll keep my fingers crossed and hope this helps.

Joe
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Tuesday, October 19th, 2010 AT 7:19 AM
Tiny
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I checked the IAC with my ohm meter and go 0's on all attempts. I have it set at 20k and then 200k and it didn't make a difference. I am going to go to the parts store and test a new one just to make sure I am running my tester correctly.

Yesterday I was driving my truck for around 20 minutes. I came to a stop and the service light came on. I ran the diagnostic and it came back with OBD 1 Code 44. From what I have found this indicates the truck is running lean.

Before I replaced the EGR I got a 45 code, but now a 44?

Thoughts?
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Sunday, October 24th, 2010 AT 12:21 PM
Tiny
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That is an interesting one. It has gone from rich to lean. Are you sure that by accident you didn't knock off any vacuum hoses?

As far as the UAC, it sounds bad.

Let me know what you find.
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Sunday, October 24th, 2010 AT 9:56 PM

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