My '93 volvo 940 wagon (regina system) suddenly began to have issues, when I start it in the morning. Just after it starts, RPM jumps like crazy between 0 and 1000, and often car can stall. Then, after about 20 seconds, RPM stabilizes and car runs more-less fine. If I restart it after this, car starts almost like usual.

Another, perhaps related issue is stalling when starting to move from red lights: when I push gas, RPM drops down and car stalls. Also it has relatively poor gas-mileage, about 16 mpg for combined city/highway, though it may be unrelated..

Any ideas where to look? Is this fuel pump/pressure regulator, or more likely it's a computer?

Thanks!

 

i'd start by cleaning the idle valve...
how's the tune up condition? plugs, wires, dist. cap, rotor?
computer is the last thing to blame.

 

It did have a slightly uneven idle since I bought it. I will try to look into the idle valve tomorrow. I've changed distributor wires some time ago. Nothing much was recently done before.

What puzzles me is the very rough start in the morning, and normal starting after this.

 

My mechanic checked a number of things but didn't find anything really wrong: no leaks, idle valve/idle motor is fine, map voltage is good, air temp sensor looks good, iac duty cycle is ok, and so on..

The only suspicion was in the oxygen sensor: the voltage there oscillates between 1.17 V and zero, with a period consistent with idle oscillations. Can it be the oxygen sensor that causes the uneven idle/poor gas mileage? Car never gave me a check engine light.

The problem is still there, moreover the idle now can continue to be uneven even when the car is warm.. Any further ideas where to look would be appreciated.

 

Hi ms000
I'd recommend looking at the entire post of "92 Volvo 740 idling issues", I have a 89 regina rex wagon as well and i've just about got the idling issue ironed out "it's alot better than it was". You said that the mechanic checked the map sensor for proper voltage but did he check or replace the map sensor with a good quality new one for test purposes? volvo regina map sensor cross references to a ac delco 213-185 or 213-1545. don't use a bargain basement grade. also check for leaks on map sensor vacuum line. there are a few other suggestion in that other post.