98 Idle problem

[eng208]

My 98 just started having a stalling problem. I did a search and see others describing the same problem, but can't find a clear solution. Not looking to just start replacing parts without some background reasoning. Here's the issue.
The truck starts fine, runs great until it gets to operating temperature. It continues to run fine while driving. However, when stopped and idling for about 2minutes or more, the idle suddenly dips and starts running rough, then catches back up for a moment before going into a cycle of low idle, then normal, low idle again. Sometimes, it will stumble and die. I have cleaned the IAC, MAF and throttle body late last summer when it did it. It seemed to make it better and has not actually cut off but a few times since then. But today, it suddenly got much worse. I sprayed the throttle body with Seafoam cleaner and let it run for a good 10 minutes, thought it was fixed. The girlfriend took it out for a drive and while at the drive thru, called and said it was idling rough again.
Not sure where to go from here. Should I order an IAC? When I pulled the IAC off last summer, I cleaned it good and noticed it had some play that didnt seem normal, but it really wasn't that dirty.
BTW, my truck has 239K on it.

 

[Kyngfish]

My 98 just started having a stalling problem. I did a search and see others describing the same problem, but can't find a clear solution. Not looking to just start replacing parts without some background reasoning. Here's the issue.
The truck starts fine, runs great until it gets to operating temperature. It continues to run fine while driving. However, when stopped and idling for about 2minutes or more, the idle suddenly dips and starts running rough, then catches back up for a moment before going into a cycle of low idle, then normal, low idle again. Sometimes, it will stumble and die. I have cleaned the IAC, MAF and throttle body late last summer when it did it. It seemed to make it better and has not actually cut off but a few times since then. But today, it suddenly got much worse. I sprayed the throttle body with Seafoam cleaner and let it run for a good 10 minutes, thought it was fixed. The girlfriend took it out for a drive and while at the drive thru, called and said it was idling rough again.
Not sure where to go from here. Should I order an IAC? When I pulled the IAC off last summer, I cleaned it good and noticed it had some play that didnt seem normal, but it really wasn't that dirty.
BTW, my truck has 239K on it.

Had a similar problem in my 98. Few things I’d try. Make sure all the vacuum hoses, specifically to the charcoal canister are correctly connected. I had one routed incorrectly and that lead to stalling. Also. New plugs and wires greatly lessened the problem. I still get rough idle now and then but no stalling. Third. Never top off your gas. It can create issues with the charcoal canister.

The plugs and wires made a huge difference. I’m going to clean my throttle body next and see if that smooths out the idle a bit more. After that I’ll replace all vacuum hoses and put in new coil. Let’s see what happens. Good luck.

 

[eng208]

plugs and wires are 12K old. I will check the vacuum lines to the evap container.

 

[Kyngfish]

plugs and wires are 12K old. I will check the vacuum lines to the evap container.

Fair enough. Mine has similar symptoms to yours. Runs fine until hot. Then occasionally rough idle until it stalls. I’ve seen threads on here that solve it with a new charcoal canister. I can’t shake the feeling it’s a vac line problem. My lines are old and cracked. If you’ve already done the iac and throttle body those are the next things I’d check. Then... injectors maybe? If I find anything that fixes it totally I’ll keep you updated. But once I checked through all the lines and replaced the plugs and wires I stopped stalling.

 

[eng208]

Ran great today, no stalls at idle. In fact, today it was so smooth idling, I had to keep looking at the tach to make sure it was running.......