Car has a rough idle, and diminished accel performance.

new parts: Idle control valve, plugs, plug wires, distributor cap, rotor.

Cleaned MAF, checked coil (checks OK), checked battery and charging system (checks OK), engine throwing no codes. Replaced air intake hose between MAF and turbo (was cracked). Still slight rough idle. Here is the strange thing, the day I replaced the idle control, rotor and cap, it ran like a new car. But only for that one day. The next morning it was back to its old tricks again, although slightly improved. For some reason, it seems to run worse on days with high humidity, which makes no sense to me. Any help would be greatly appreciated.

 

Some one else can give you ideas, but this is what worked for me:

How many miles on the car? over time...wear and tear on the valve terrain can cause rough idle.

I had ~255,000miles on mine and it idle "rough" all the time. we checked the clearances, and where suprized to find that the shims where touching the cam (ie. no clearnance).
Then we ordered the shim kit from IPD (~$50), BOOM, Idles like a brand new car.

You should check the valve clearances:

Valve clearance, cold engine 0.012-0.016" 0.014-0.016"
inlet and exhaust (0.30-0.40 mm) (0.35-0.40 mm)
Valve clearance, warm engine 0.014-0.018" 0.016 0.018"
inlet and exhaust (0.35-0.45 mm) (0.40-0.45 mm)

 

Try a new air filter.

 

Has new air filter. Also, just had valves adjusted not more than 5 weeks ago. Any other ideas?

 

Did you pull the codes off the ODB? How about the o2 sensor?

 

He said no CEL, but should still check.

 

Yes, check codes. I would also reset the ECU, disconnect battery overnight. SOmetimes after you replace a few bad parts on these cars the computer can benefit from starting fresh or it continues to use "corrupt" data stored from the old, bad components. These ECU's have a fair self learning ability.
If that is all O.K, I would check for vacuum leaks.
EDIT: And don't expect a glass smooth idle from a redblock, they're just not up to it. They're an inline four which is not a smooth engine and they're a 30 year old design. Aim for acceptable!

Regards, Andrew.

 

The OBD is not showing any codes, the only one I have gotten recently (last 3 months) is 3-1-2 (ground wire to the computer or something like that), but that is cleared now and has not returned

I have not tested o2 sensors. Does this car have one or two? Also, does anyone know what the reading should be on my ohm meter to know they are ok? or should I say, How do I check them to see if I need to replace them?

Just to confirm: Resetting the computer requires leaving the battery disconnected overnight. Is there a more definitive amount of time than overnight?

I understand it wont be super smooth, I'm just looking to have it not feel like its going to die or rattle the interior apart.

 

Click Here for the O2 sensor
312 is the knock sensor.

You can remove the battery for ~30mins....or I think you can remove fuse #1

Also check out this site: http://www.vcoa.org/700-900-faq/FAQSummary1.html
Has a lot of good info.

 

Yes, a half hour is enough fo an ECU reset. I just say overnight because it's easy for people to do. You know, come home, disconnect battery and reconnect it next morning.....

Regards, Andrew.

 

I agree

 

Ok, so when I reset the ECU, it works better for a short time. like 20 miles. So I replaced the O2 sensor and the coil, and it works better still, yet problem not eliminated. I think its an electrical issue for sure. And probably a spark issue, because as someone pointed out to me in another thread it might be misfiring at high RPM. Which means that its probably misfiring as soon as the turbo kicks in. Which means that its probably a spark issue. So I cleaned all the ground points I could find, and just for fun ran seafoam through it and changed the oil. It runs better still. So today I think I'm going to pull out the spark plugs, and re gap them to a closer than spec gap to try to eliminate the high RPM misfire. Can anyone think of any potential issues that might arise as a result of re gaping the plugs?, other than an obvious loss of power. Any other remedies for the misfire? Any other suggestions?

 

I think the gapping is supposed to be between 0.7 or 0.8mm??

 

the moisture thing has all the earmarks of plug wires but they're new? What happens when you mist around the ignition? And what did the cap look like? was the seal leaking badly?

 

Clean the throttle body. Just had my 93 940T done it made a huge difference.

 

I cleaned it yesterday, and it made a slight improvement. Check my latest post for a complete list of things replaced. Its a long one.

 

man, the cap looked like it was 225000 miles old. Dirty, caked with all kinds of dirt. the seal was not leaking abnormally, but was also replaced at that time. and yes the plug wires are new, OEM Volvo wires. when I mist around it with water, nothing happens.

 

Thank you for the ECU info! Chilton's method was not working. I got tired of doing the same thing over and over hoping for a different result.
Peace.

 

Hi to reset ECU I ,open the door window, disconnect earth lead from battery, turn on ignition, "splash" earth lead to battery terminal a couple of times with ign on,reconnect battery--done.

 

Hi check the ignition ballast resistor - remove it, take it off its mounting plate, remove any corrosion between th two, and at the back of the mounting plate, put back together and remount cleaning contacts in the module and plug,--it worked for me