I have a 1993 Volvo 240. When I’m driving in the car is cool, it drives perfectly. As soon as it starts to get warmer, the car idles a lot like every 15 to 20 seconds. When I put it in reverse, it starts idling really rough.

We already changed out the ignition control module but it didn’t help

I feel like if it was a vacuum problem, then it would happen when it was cold and hot.

What do you think you could be?

 

It could be a leak in the air intake system - including vacuum leaks. When the engine is warm, the ECU looks at the oxygen sensor to determine the amount of oxygen in the exhaust along with information from the air mass meter to determine how much air is going into the intake. Prior to warm up, the engine is in "open loop" mode and doesn't look at these sensors. So having an air leak (including vacuum leaks) allows unmetered air into the intake and would affect the system only after warmup.

Several items to check:

- Engine codes. Have you read your engine codes?
- Check for leaks in the air intake system. Most importantly, check the hose that goes from the air mass meter to the throttle body for leaks. Any leaks in this hose will let in unmetered air and wreak havoc with your idle once the engine is warmed up.
- Check your idle air controller to ensure it is functioning properly. It may need to be cleaned
- Check the adjustment of the throttle position switch.
- Check your throttle body for carbon build up. It may need cleaning as well.

 

I’m not sure if I explained it correctly. It’s a really rough idle like it wants to stall. I’ll be in the car in the car drives and it like jumps. It’s jumping like the timing or something. I don’t know how to explain it. Sorry. Thanks for your help

 

Have you checked your engine codes? It still applies. You say you have a rough idle, is it too low? A rough or lumpy idle can be caused by vacuum leaks so I still wouldn't rule that out entirely.

 

Check youtube for some RobertDIY: vids on the engine coolant temp sensor

The temp sensor feeds into the ECU to enrich the mixture when the engine is cold. Does your temp guage behave normal or does it seem to be off a bit? (

When you talk about a lumpy idle - ie almost stalling then revving, that can be as simple as the ECU trying to adjust for the out of range engine speed. As act1292 pointed out, check for fault codes. Cars prior to 1996 don't support the OBD2 standard but you may have a diagnostic port with a jumper/button/LED that you can use to flash out the codes.