1996 850 Random Misfire All Cylinders only at Idle

freebirdchampion · Post by **freebirdchampion** » 28 May 2015, 15:24

Hi All,

I'm new here and am in need of some help.

I recently purchased a 1996 Volvo 850 GLT with 195,000 mi. I have a random misfire code P0300 and a missfire on all cylinders (codes p0301-p0305) only at idle.
If I reset the engine light on the hwy I can drive for hours without a problem and it runs great. As soon as I exit and come to a stop light it immediately throws the same codes.

Here's what I have done so far.
Distributor cap/rotor, wires, plugs, checked exhaustively for vacuum leaks, checked fuel pressure at the rail which was good 50psi, replaced fuel pump relay, did MAF test and swapped out a used one just in case, swapped ECU, tested out both cam and crank sensors and cleaned idle control valve/ throttle body ( they were disgusting ((hard carbon build up in the throttle body manifold), and changed coolant temp sensor which was out of spec.

The problem continues.
Hard starts unless the car has just been running and a hard all cylinder misfire. I'm so frustrated! My PCV system is clogged (just did the glove test). Could this be the problem? Any input is appreciated. Thanks!

Post by **erikv11** » 28 May 2015, 17:03

One common cause of stalling at idle is vacuum leaks. Check all vacuum hoses carefully, especially any that are old and rotting. With everything you have looked at, my money is on vac lines or a dirty IAC (Idle air control valve).

https://www.matthewsvolvosite.com/forums ... =1&t=65002

The IAC can be cleaned by simply spraying in carb cleaner, and swishing it until you hear the spring-loaded valve flopping back and forth cleanly. Wear eye protection.

freebirdchampion · Post by **freebirdchampion** » 28 May 2015, 17:43

Thanks for the response. I thouroughly cleaned the iac and i feel ive really rulled out vaccum leaks. At a lost, but i agree it does seem like a classic vacuum leak. :/

Post by **erikv11** » 28 May 2015, 17:54

Maybe try the starting fluid or propane torch trick for finding vac leaks? It should be sizeable one if there is indeed a leak, those methods should work.

draser · Post by **draser** » 29 May 2015, 06:27

Can you pull the plugs to see if engine runs lean or rich, or scan live data and post back?

freebirdchampion · Post by **freebirdchampion** » 31 May 2015, 22:06

Woooo! Figured it out. Timing was off---by a lot! Thanks previous owner for installing the new belt wrong. She is running perfect