Odd Rough Idle issues, car runs great in gear, hauls a$$ gets good gas milage but if I put it in neutral, it idles very rough. No codes.

History, motor has 107k and was just installed in C70 with 160k. My plan is to run this car another 100k, so before I installed the motor I went through it thoroughly: complete cleaning of pvc system, throttle body, pulled pan and cleaned, did o-rings, new main seal, new intake and exhaust gaskets, exhaust to turbo gasket, new plugs, new Bosch ignition coil set. I have checked and rechecked the vacuum hoses, many were replaced. I have several MAFs which I have tried. Had an issue with the cam timing valve so it was cleaned thoroughly. Injectors appear to be all firing nicely, I turned the rack upside down and cycled the starter motor.

Any thoughts?

 

They always say to unplug your MAF whilst idling rough and see if something changes.

Why do you have several MAFs?

 

I will try the MAF but I doubt its the issue because I was listening to it carefully yesterday and what is happening is that it runs great then all of a sudden one cylinder drops out for a second or few then comes back. Strange huh? That is why I replaced all the ignition coils. When I drive it though it runs fantastic, gets great gas mileage and pulls hard.

I went through a nightmare a couple of years ago where my computer was throwing the fuel matrix off so bad it wouldn't start without me rebooting the computer. Turned out to be an intermittent short in the temp sensor wire. I got a few MAFs and every kind of sensor I could find in the Junk yard to try to troubleshoot it. With the new motor I purchased, I got more sensors so I have a box full of MAFS and sensors...

 

BTW, has anyone ever replaced the wiring loom that feeds the ignition coils and injectors? Mine is pretty baked. Is it a fairly isolated loom or is it part of the larger body loom?

 

I don't know about the wire loom. You'd think the part which branches off and reaches into the engine (where it'd be subject to heat) would be designed to be replaceable.

I know that our cars have Idle Control Valves.

Locate yours and unplug it during a spate of rough idling and see if anything changes.

 

you can get injector harness off ebay, they are cut from the main harness so you'd need to solder them .
Injector test light might help, less than $5 from the major volvo supply houses.

Does vadis show where the rough idle is coming from, could be ignition, throttle body or injectors and maybe other causes too.

 

interesting you should talk about testing the injectors, my simple way of doing it is removing the connector and see if it changes the idle. Turns out yesterday when the car started idling poorly I started pulling injector plugs and found at the number one injector made no difference plugged in or unplugged. So I replace the injector and the same thing still happens.
next I’m going to swap injectors number one and two and make sure that I didn’t get a second bad one but I have a feeling that my problem is in the electrical side of the number one injector circuit. I’m guessing that circuit goes all the way to the computer, so if I can’t find any bad wiring or questionable wiring
I may have a computer problem on my hands. I have not hooked it up to Vadis, our Local Volvo whisperer has not opened yet thanks for your help any thoughts you have a definitely appreciate

 

So last night it threw an 0205 injector circuit code. Now I have to figure out what's going on. Since I replace the injector (with a used one from an old motor I took out) it still has the problem. I am in a quandry, have no idea other than to work to the computer thoruhg the wiring to see if there is a chafe. Any other thoughts? I will sway 5 and 1 injectors just to see if by chance I hit the Volvo lottery and got two bad injectors.

UGH!!! After all I have bene through with this car new motor and all, I keep dropping money thinking it will finally give me 100k miles but it just keeps going. Did I mention I'm replacing all the tie rod ends this weekend, the alignment... UGH!

I really think I'm close though, the car runs great, very fast good milage but at idle it drops a cylinder.

 

make sure the replacement injector is a correct match since the impedence may vary. You can also have your injectors tested/cleaned - just google for a local shop. That said, you should be able to test if you are getting a pulse to the connector to the injector - if not you may have a wiring harness issue or a connection issue to the ECU etc. May not be a bad idea to pull components out and clean their connectors with some electronics cleaner then reconnect.

 

No difference in idle when injector unplugged ?
that doesn't prove its the injector.
It could be the coil or plug too.
You probably got a code because you disconnected the injector when it was running.
Vibration at idle is also caused by bad motor mounts.