I bought my '94 940 Turbo in April 2010 with 94k miles. It's currently at 105k miles. I've been dealing with an annoying problem that my Volvo mechanic can't seem to pinpoint. I'm willing to spend the money to fix it. He just can't seem to figure it out, or isn't willing to put the time and effort into resolving the issues. He's had it now 3 times and gives me the same answer every time, "I don't see anything wrong."

During the hot summer months that I've had the car, when it was 90+ degrees out, the idle was very erratic. Some days I'd start the car, and the idle would be around 600rpm, causing the car to vibrate annoyingly. Other days I'd start it and it'd idle as high as 1600rpm. On a couple of occasions, it idled high, as mentioned, and smoke poured out of the exhaust until the engine warmed up. Since the weather has been colder here now, ranging mostly 30-50 degrees out, the engine is consistently idling too low, causing the car to idle very rough and vibrate.

At the recommendation of my mechanic, I had him replace the coolant temp sensor and throttle position sensor. He said codes came up for both. I also had him replace the fuel filter and clean the flame trap. I did a full tune up myself, using good quality parts from Bugicord and Bosch. None of the above mentioned helped fix the rough and erratic idle. After 8mths and 11,000 miles of driving it like this and half a dozen trips to the mechanic, I'm getting seriously annoyed. This issue combined with a steering issue (I'll post separately about that) are making driving my Volvo an unpleasant experience. I love the car, so help me out if you have any suggestions. This is the 3rd 940 Turbo I've owned. The last two had higher mileage and ran MUCH more smoothly.

 

Hello PBB..

You mentioned "hot summer months"...and "90+ degrees out".
I am only assuming that the A/C is ON?
If so, I am looking to correct this problem also.

Just came across this TSB, hope it helps

My 94' 940 wagon experiences erratic Idling when A/C is on.
Should be approx 750rpm an norm. Cannot find info on what type of capacitor??

1994 Volvo 940 L4-2.3L SOHC VIN 88 B230F
Engine Controls - Decreased Idle Speed When A/C Engages
SECTION: 2
GROUP: 28
NO.: 913
DATE: Feb. 1995
RE:
Momentary idle speed decrease when A/C engages B230F - Regina/Rex 700/900, 1992-94 *
REFERENCE: SERVICE BULLETIN 28-910
This Service Bulletin replaces the earlier SB 28-913 of July 1994, which should be discarded.
Momentary Idle Speed Decrease
A momentary decrease in idling speed when the A/C compressor cycles on may be corrected by connecting capacitor kit, P/N 9128921-5. to the MFI
control unit lead.
Note!
The above applies only to cars with MFI control module, P/N 6842882-0. (5003860-3), P/N 9146261-4 (5003946-0) or P/N 1271709-6
(8601056-8).
* May apply to earlier models if above mentioned MFI control module has been installed or the existing control module has been updated.
Installation of Capacitor Kit
The capacitor kit can be used only in combination with MFI module. P/N 6842882-0, (5003860-3). P/N 9146261-4 (5003946-0) or P/N 1271709-6
(8601056-8).
Disconnect:
^ battery ground lead (if still connected).
Important!
MFI module must be dead when connector is disconnected or reconnected. otherwise module may be damaged.
Expose:
^ MFI module located at right-hand end of firewall panel.
Disconnect/Remove:
Removal and Installation of Capacitor Kit at MFI Control Unit
^ module connector.
^ cable tie securing protective rubber sleeve on harness. Push back sleeve approx. 10 cm on harness.
1994 Volvo 940 L4-2.3L SOHC VIN 88 B230F
^ screw in end of connector and separate connector halves.
Connect/Attach:
Removal and Installation of Capacitor Kit at MFI Control Unit
^ black-green capacitor lead to terminal 14.
^ capacitor red-green lead to lead connected to terminal 15, using Scotch-Lock clip.
Capacitor kit contains two Scotch-Lock clips.
^ Red clip should be used on models to 1991 inclusive.
^ Blue clip should be used on models from 1992 on.
^ Reassemble connector using screw in end.
Removal and Installation of Capacitor Kit at MFI Control Unit
^ Secure capacitor to harness with electrical tape, with capacitor facing firewall.
^ Wrap complete area between protective rubber sleeve and connector with tape.
Reconnect/Reinstall:
1994 Volvo 940 L4-2.3L SOHC VIN 88 B230F
Removal and Installation of Capacitor Kit at MFI Control Unit
^ connector to module.
^ other components which have been removed.
Test engine performance and reset electrical functions including radio code and/or any DTCs.
WARRANTY STATEMENT: Claims may be submitted under the New Car Limited Warranty when a manufacturing defect is present using claim type:
01
28924-2 Capacitor

 

Is the air mass meter you mention the same as the mass airflow sensor, or two different parts? I read online that if you unplug it while the car is running and the running condition is not affected, it means the sensor is bad, but if unplugging it makes the car run horribly or stall, the sensor is good. When I tested this out by unplugging the sensor, the check engine light came on and the car stalled, so I'm assuming the mass airflow sensor is fine.

 

[QUOTE=Nodrive55;252710]Hello PBB..

You mentioned "hot summer months"...and "90+ degrees out".
I am only assuming that the A/C is ON?
If so, I am looking to correct this problem also.

Just came across this TSB, hope it helps

My 94' 940 wagon experiences erratic Idling when A/C is on.
Should be approx 750rpm an norm. Cannot find info on what type of capacitor??

Thanks for the TSB, but I don't think it applies to my Volvo's problem. The idle is erratic no matter if the AC is on or off. I mentioned the different idle behavior in relation to the outdoor temperature because it seems to affect the idle condition.

 

i had similer problems after i did a tune-up on my 93 940T and i put bosch plugs in mine and it ran choppy as hell took the plugs out put NGKs and the car ran fine and haven't had trouble since then. I had a tech tell me that bosch plugs are bad unless you put them in German cars. IDK just wat I had happen. Hope it helps

 

Has the throttle plate been cleaned? Has the oxygen sensor ever been replaced? Have you done a resistance test on the Idle Air Control Valve? Those may be a few good places to check.

 

940 engine idles rough?
Clean the idle control valve with carburetor cleaner,remove the two hoses, take off the electrical connection and lift it out of the rubber gage, in this country we call it an air flow meter but it controls the idle, spray in both holes, push back the piston inside and spray there then dry off, clean your flame trap and all the hoses and clean the breather box under the inlet manifold and clean the throttle body with the carburetor cleaner