Misfiring at Idle
 

Hello,

Been ages since I was last here. Hope y'all can help me out.

OBD I A2

Code:

514 – engine cool fan low speed signal

543 – misfire one of cylinder

451 – misfire cylinder one


So I had an engine light on a few weeks ago. Checked the codes as it appeared in the mentioning above. Cleared the codes. Checked plugs, wires, distributor cap. All appeared to be fine. Clean the points on the cap. Thought fuel injector for cylinder one was faulty and replaced it with new one. Engine still ran rough. Tried to unplug the MAF and it appeared to make engine run smoother, but personally can’t determine if the MAF is faulty or there is a vacuum leak. I tried to spray carb cleaner around the intake manifold the best I could and I see no change on how it ran during idle.


Took it the the dealership, they replaced my plugs and did a compression check. All cylinders were 175, besides cylinder number 5 was at 140. I personally might try do a compression test later to see what the difference might be if I do it dry or wet, but I doubt it would have that much of an effect to cause it to misfire, would it?

Furthermore, when I was about to remove the fuel rail, I tried to release some of the pressure at the end of the rail and no fuel came out. Loosen the nut to the line to the rail, no fuel spilled out really. Just a little bit. Clogged fuel filter?

Driving the car, it is completely fine.Just at idle it gives a few rough shakes every now then and you can here the car occasionally burble or goes putt putt, bc of the misfire.

Thanks for any help.

year / model of the car (ie turbo/non-turbo)? Any other symptoms like long cold cranking? Does it seem to run better hot than cold? Anything odd with the temp guage to suggest an ECT issue? Not sure if checking the wires/cap rotor will show you the problem - I once had a bad wire that was corroded inside the boot. Only saw it because I started the car in a dark garage and saw the arcing. Did you replace the rotor/cap/wires? My recommendation is to do replace the wires and cap for starters, then I'd put a pressure guage on the fuel rail (see RobertDIY's vid on you tube) to rule out a fuel pressue issue. Next would be to clean the MAF and the idle air valve with MAF cleaner and see if that changes anything. As to the vacuum leak, that's certainly a possibility but my experience is - you may need a smoke test to see something that's not so obvious but in my experience this would cause an idle fuel trim code (ie a 2-3-2) but it could be worth the cost if you can't spray around and find anything.

It's a 95 Turbo. No long cranks. Starts normal, drives normal. Just idles bad every few seconds. Seems to run a little smoother when it warms up, but hard to tell. Physically you can see the engine shutter more when it's colder it appears. But on like a cold night you can actually see the exhaust fumes have occasional burst of air coming out of it if I had the MAF plugged in even if I had the car up to temperature. Not plugged in, runs fine, and can also see that it is, because now the exhaust fumes come out continuously. Temp is normal, no arcing with the wires that I see. Wires and cap only has 40k miles on it, so not too crazy. Already cleaned the MAF. I'm going to have to look into that idle air valve later. Haven't thought of it before.

There's a lot of plumbing between the MAF and the throttle on a turbo. Lots of places for a leak.

I doubt it some looseness would damage the intake manifold gasket itself - not like a lot of heat like on the exhaust or pinch could be going on - just some air. question is whether the surfaces were clean when the manifold gasket was installed in the first place. Now that you've retorqued the bolts, did the situation improve? If not, maybe time for a smoke test.

volvotips.com is a good resource for interpreting the OBD1 codes and some diagnosis triage procedures. Still sounds like an air leak. Did you spray around the vacuum tree (under the throttle cable spool cover), check for PCV pressure (glove test on the oil intake), There's a Robert DIY vid on Youtube on how to make your own smoke tester but I'd probably ante up the $100 and have a shop do it. the problem could be anything where there's vacuum - brakes, EVAP system etc as well as in the boost tubing, intercooler etc.

Well you need to run some tests then. Could be quite a few things but before you start guessing parts, and you've done all the visual stuff, I'd still invest the $ to have a shop do a smoke test to rule out air leaks. Did you check the fuel pressure at idle to see if its steady? Is the idle valve / throttle body clean? Any signs of an exhaust leak? Seems like something is messing with the fuel/air mix at idle. air leaks/exhaust leaks are common, dirty intake parts also, weak spark etc all need to be ruled out.