I have recently developed an odd issue with my 1994 940 non turbo wagon. This happens every time it rains or if there is very high humidity. I can start it up and it will idle smooth for about 3-5 min. Then it starts to run rough, surging Idle (from 500 to 1000 rpm) the engine will have no power ie. pressing the accelerator does nothing. No increase in rpm at all. There is a "sweet" spot at about 1/8-1/4 throttle where it has power if you hold it but before or after that point nothing. It will exhibit this condition for about 5 minutes then poof the engine runs perfectly fine with the exception of mild ilde surge (about 100 rpm range). I have replaced the usual plugs, rotor, cap and wires with correct type...bosch and bourgicord (sp?).

I purchased some throttle body cleaner and was going to go that route but to me it seems like an electrical issue seeing it only happens during wet/moist conditions. I have read thru alot of posts but haven't read anything like my issue.

Can any of you experts or anyone that has had a simiar experience direct me as to what I should look at/test next. I appreciate any assistance you can provide.

te any assistance.

 

no codes on the diagnostic block?

 

I have seen the diagnostic box but never have used it due to lack of knowledge. I see there are 2 boxes but I only see what appears to be a jumper pin attached by tether on only one of them. I'm not quite sure of the steps. OBDII has spoiled me.....

 

OK so I looked up the procedure but found one for 89-93 models. I have 2 diagnostic blocks. One is black labeled A with the push button...the other is grey and labeled B.
I got the following codes out of block A. I did not check B or any other pins in block A.

Position #2 212 Oxygen sensor signal ( I knew this needed replaced)
Position #6 111 No fault

I noticed there was a wire in position 3 but I saw no mention of it on the procedure.

This is the LH 2.4 fuel system. Will the O2 sensor really cause this issue during wet conditions? I knew the sensor was bad for a while but didn't have these symptoms until about 3 weeks after I put in new plugs, cap, rotor and wires.

Anything else I should inspect?

 

the other positions are for things like ABS, SRS. the 2nd "B" block is for stuff that wasn't allocated a pin on the original (A) block (automatic climate control?), and you use the same jumper with it. pins 2 (fuel injection) and 6 (ignition) on the A block are the only important ones...

its possible your O2 sensor is sending wildly out of range signals that change when its wet and this could throw the engine off ... the MAF/AMM (mass air flow meter aka air mass meter) is the other thing that comes to mind.

or really, any sort of connection thats getting wet and poorly insulated could throw things off when it gets wet enough.

 

Bad hood seal = water in dist.

Spray water on plug wires at night to check for leaks.

Only use bougicord wires, Bosch cap and rotor. Everything else, especially wires, suck and can give probs.

02 sensor is ignored at start up till engine has warmed and enters closed loop.

 

That was the first thing I did was purchase the bougicord wires. 2 of the wires I replaced were actually hollow about the last 2-3 inches on the plug end. The carbon rope core was burnt and gone. Couldnt believe it ran as well as it did. I cant remember if it was a bosch cap or not tho.

How can I check/test the MAF/AAM. I will replace that O2 sensor next week for sure. I'm still averaging 25 mpg..not too bad considering 225k plus how ever many they put on it before I fixed the speeometer.

Thank you for you comments/suggestions.

 

Start with 02 sensor.

Best way to test for bad maf is to unplug it and go for a drive. If power is back, bad maf!

02 sensor you can check with multimeter. Swings back and forth between 0-1v. Stuck at either extreme once its hot means its bad.

 

The O2 sensor won't cause what you are trying to fix.

Unplugging the MAFS definitely won't bring "power back"! If it did, why have a MAFS in the first place. Unplugging the MAFS causes a "limp mode" normally.

I would change the plugs to plain copper NGK.

Also, moisture in the distributor is a good thing to address as suggested.

 

I did put in new copper core plugs about 1000 miles ago. They are not NGK but I did specify copper core. I am going to pull the dist cap and inspect for any damage to the wires in there as well as look for signs of damage or moisture. As for the O2 sensor I know it is not providing a good signal and I have that repair scheduled in the near future. I was fairly confident the O2 would not really cause the issue at hand but stranger things have happened.

On another note.....what should happen when you disconnect the vacuum line on the fuel pressure regulator? I'm getting my toes wet so to speak in the world of volvo's and am just checking things out. I notice no change in engine speed when removed as long as I plug the vac line. Logicall it should effect pressure flow but in what way? What should the pressure be on this LH2.4 system when fpr is hooked up and working properly? Sorry for thr OT question here. I just want to learn what I can about these awesome vehicles. Thanks in advance.

 

Get NGK Copper plugs, they are only about $1,29 ea.

Nothing should happen if you disconnect the vac line on the FPR! If the FPR is leaking there should be gas smell or gas coming out of it. The FPR has nothing to do with your issues--don't waste your time! The FPR regulates mainly excess pressure, releasing (returning) the excess gas back to the tank. It also maintains pressure when the engine is already hot thus if it is failing you get slow starts (much cranking) once car is warm. If the car is cold, the ECU sends extra gas so starting is not affected by the weak FPR.

 

Also check battery terminals and ignition power stage/amplifier connection. They are near the hood gap=rain encroachment.

So is your hood seal good above the dist? One dude put a paper towel on his dist, closed hood, added garden hose, then noticed wet paper towel after. Clever test!


Also inspect RPM sensor on bellhousing top for fraying or water encroachment and also at it's plug.