1996 850 GLT Very Rough Idle

EuroLo89 · Post by **EuroLo89** » 09 Mar 2014, 18:48

Alright guys, as the title states I have a 1996 Volvo 850 GLT with an M56 trans. I've had a problem of a rough idles and cutout or the car stalling after it warms up. Sometimes it idles down low enough and makes the oil light come on, but as soon as the rpm's go back up the oil light goes off. I thought it was a fuel related issue and have replaced the fuel pump, fuel pump relay as well as the injector relay; but that did nothing for me as the issue continued and seemed to only get worse. Then I did a tune up replacing the spark plugs, plug wires, distibutor cap, rotor button, air filter, oil filter, oil, fuel filter; but still no luck with resolving this. Questioning the idle air control valve, so I took it off and cleaned it thinking that would help, but seems to only have made it even more worse.

Can anyone help me figure this issue out before I go spending another $500.00 in parts, Any and all help would be greatly appreciated. Thanks...

Post by **rspi** » 09 Mar 2014, 18:51

Does the car have a CEL?

EuroLo89 · Post by **EuroLo89** » 09 Mar 2014, 19:26

No CELS when I checked the other day.

Post by **rspi** » 09 Mar 2014, 20:09

If the bulb in the CEL works and you have no codes, I guess you should check compression.

Post by **erikv11** » 09 Mar 2014, 23:40

Checking compression is always a good idea, but low compression pretty much always throws a code. Be prepared to keep looking for the cause ...

EuroLo89 · Post by **EuroLo89** » 10 Mar 2014, 02:08

Alright, well I guess I'll go buy a compression test kit.

Kecy · Post by **Kecy** » 10 Mar 2014, 04:16

You could have a vacuum leak somewhere, check before you go spending $$$ ..

Post by **erikv11** » 10 Mar 2014, 04:29

^^^ this.

EuroLo89 · Post by **EuroLo89** » 10 Mar 2014, 09:36

I've already checked the vacuum lines and just ordered a new iacv last night cause I know mine is shitting out.

Post by **erikv11** » 10 Mar 2014, 10:02

I'm sure you want to fix this ASAP I don't blame you, but if your description is accurate then it's not compression. Just chasing every idea you will fix it eventually, but it will cost you. Here's my thinking: nine times out of ten (99 out of 100?), bad compression is bad all the time, not just when the car is hot. And stumble due to low compression pretty much *always* gives a misfire code in the offending cylinder. So go for it as it is not so expensive for a gauge and it will serve you for years, "just sayin" though.

If you are sure about vacuum, my next stop would be electrical. As the car gets hot, the resistance of all electrical parts goes up. Check all of the grounds including where they contact at both ends, and check the positive cables from the battery. Both ends.

Hopefully it is the IAC, since you already sprung for a new one. Oh, check the TPS for sure. Keep checking for codes.