1988 Chevy Silverado Intermittent rought idle

I talked to the people at the auto parts store and they said that with my year of truck the computer does not store the OBD 1 codes. The light has to be on to check it. I have tried to get it to come on, but to no avail so far. I checked all my vacuum hoses and the are all connected, and not broken or cracked. Whether they are leaking or not I don't know. Now the truck has a rough Idle all the time. I thought it was the O2 sensor so I replaced that and it seemed to help a little but not much. The auto parts store suggested that it could be the EGR valve.
Any help would be greatly appreciated

I read almost all of the posts on rough idle, and came up with egr, or iac. I was thinking the IAC because the rpms dip when I let off the gas and turn the steering wheel or put it in gear. I am going to pull them off in the morning and check to clean or replace. I will let you know how that works out.

Matt

I pulled off the iac and cleaned it good, looks shiny and close to new. There were some rub marks on the tip of it but didn't look too bad. I put it back in and started the truck. I ran a little better but still rough and back firing. I pulled off the egr and cleaned it. I noticed that one of the nuts that was holding the egr was only finger tight. I put a new gasket on and put it all back together. It runs smoother now and not so doggy when I turn the steering wheel and brake. It is still back firing though. You can hear it when it idles. Dah dah dah boom dah dah dah dah boom boom (my engine sound effects). Not really loud but you can hear it in the idle. When I speed up with the pedal 3/4 of the way down and let off it back fires a couple of times. If I rap the gas hard it also back fires. I don't know if this is the rotor, or the distributor cap, but im thinking it is electrical. Any suggestions?

Thanks again, we are getting there

The back fire is coming from the exhaust. I replaced the cap and rotor and wires and plugs two or three years ago. I am going to pull the cap and the rotor to have a look and it. I will also check with the parts store and do the compression test if they have a tester for my truck. I will send and update later.

Thanks again

Ok I did the compression check and this is what I got (148, 150, 135, 138, 140, 150, 130, 148) They all seem to be within the acceptable ranges. Drove it still have loss of power, back firing, missing. I am going to check the rotor and distributor cap, tomorrow morning. I ran out of light tonight.

Thanks

I also noticed today that my temperature reading on my instrument cluster is not registering a temp. The rest of the gauges are working fine and the truck is warm, but I don't know the temp. Will I have to replace the entire cluster or just the temp or could there be another reason its not reading the trucks temp?

Thanks

matt

I got the temp sensor working again. I also checked the distributor cap and rotor. They were used but still looked new. There were no carbon marks inside the cap. I cleaned them up and put it back together. The truck runs better but still has a miss. The idle will run smooth and then fall off, and pick back up to normal idle. If I pop the gas if back fires. It runs worse when its cold, then better when warm but still misses. I am not sure what to do now.

Any suggestions?

Thanks

Well so far I have checked the distributor cap, rotor, plugs, wires, and no problem. I did the compression test. I pulled the EGR and IAC, cleaned both of them. Replaced the oxygen sensor. I checked all the vacuum lines for breaks, nothing. I have not tested the vacuum pressure of the lines or the pressure of the EGR to see if its functioning properly.

This is the update for now, I will try anything you suggest this weekend. Just let me know

Sorry to hear about your dad.

This weekend I drove to my friends place to replace my CV shafts. On the way there the service engine soon light came on so I pulled over shut the truck off stuck the paper clip in and got Code 32. I looked in my chilton book and it said egr vacuum loop is bad. I pulled off the line that comes from the MAP sensor and had a friend hold his hand over the end and I reved the engine and he said there was vacuum pressure. So I think my EGR valve is shot.

Would you also think this could be the problem?

Also My power locks don't work and only my drivers door power window works. I tested the motor on the passenger side and it works. But there is no power to the switch. On the drivers door there is power to the passenger window switch but when I plug in the working switch it doesn't roll the window down. So I from what I can tell there is no power to the passenger door at all. And the drivers door I believe is just switches, but I don't know if the bad switches in the divers door would affect the passenger door.
Suggestions?

Thanks again

matt

I pulled off the EGR and cleaned it good, cleaned the opening on the head too. Put it back on and it still stumbles at idle. I pulled the hose that runs from the MAP sensor to the EGR and had someone hold their hand over it while I reved the engine, and they could feel the suction. I think my EGR I bad, but I'm still not 100% sure.

I tried working switches in the sockets. I got the power door locks to work, it seems that problem was the switches on both doors. I checked for power to the plugs and the plug on the drivers door that controls the passenger window has power, but when I put in a working switch the passenger window doesn't work. I checked for power on the passenger door window plug and it has no power but the door lock plug does. I put switches in the drivers door passenger window and the passenger door window and neither work. I tested the passenger door window motor and it works in both directions.

Suggestions?

Thanks again

I pulled the vacuum hose off of the EGR. Plugged it and reved the engine. It still had a small back fire. I put the vacuum hose back on and reved the engine and it back fires when reved. Both ways the has a rough idle. I hook up the vacuum hose and reved the engine while holding the EGR and it didn't move. I pushed on the EGR and it tried to kill the engine. It lost power and almost died both times I pushed on it.

Is there anything else I could try or is this were my problem is?

I tried working switches in the window control sockets. I checked for power to the plugs. The plug on the drivers door that controls the passenger window has power, but when I put in a working switch in it the passenger window doesn't work. I checked for power on the passenger door window plug and it has no power but the door lock plug does. I put switches in the drivers door passenger window plug and the passenger door window plug and neither roll up or down the window. I jumped the passenger door window motor with a battery and it works in both directions.

Suggestions?

Thanks for all the help!

Well I cleaned the EGR and the part of the intake were it sits. The truck still runs rough. It runs better if I have the vacuum like that runs to the EGR plugged with screw, but even then it still is rough. When the vacuum like is plugged the idle will be steady then drop then come back to steady idle. When I have the EGR hooked up it almost seems like its missing, and backfires more.

I checked the wiring from the door to the door jam. No cuts or anything. I pulled the boot off and pulled out the wires and found a connector there. I unplugged the connector, and tested it. No power from the connector either. I am thinking it must be closer to a control panel. I don't have a wiring diagram for the window system. The chiltons wiring diagram doesn't have the power window or locks. So I don't know were the power to that window comes from.

Suggestions? Thanks