occasional low idle...
 

1994, 940 wagon, automatic with 200k. The check engine light has been on for a couple of months. All fluids are fresh and at the correct level. When the light first came on I disconnected the battery and it would stay off for a while. Not any more.

I drove it 200 miles last week on an interstate run to Atlanta. It's been years since I have driven it and it runs out like new. The car at normal idle is around 900 rpms. 2 or 3 times I noticed it idle around 4 to 500 rpms. When I gave it a little gas it would settle back to normal idle. Any connection between this and the check engine light?

I going to repair the back door of her wagon tomorrow (when the door shuts the panel is not secure at the top). I have an ebay "kit" for repairing.

So if my intermittent rpm issue and check engine light are unrelated any advice on troubleshooting would be appreciated.


Thanks in advance,


moms940

you have a diagnostic reader box under the hood that reads out in LED blinks (you count blinks to get the codes). you should see what your codes are, and you can reset them there, if they come back, then they are definitely worth diagnosing.

see... Engine and OBD Diagnostic Codes

your occasionally dropping idle could be a gummed up throttle not hitting the throttle idle switch, or a gummed up idle air controller. I'd investigate the throttle body switch first, its easier. the throttle should be adjusted so its fully closed, and the switch makes positive contact. opening just a bit of throttle opens the switch with a distinct click.

with the engine fully warmed up and all accessories switched off, unlpug the idle air controller, restart the engine, and it should idle at 400-500. there's a screw adjustment to fine tune this. with the IAC plugged in, the idle should be about 700 rpm with a warmed up engine, even with lights, a/c, etc on. a cold engine is more like 900.

nice, now I have a starting place
 

pierce, thanks for heading me in the right direction. Off to Mom's now...

What I learned today
 

Drivers door tag states a 9/94 build date. Sorry, I said it's a 94 but that would make it a 95 model. I'm guessing a 95, 940 troubleshooting codes is completely different as this car did not have the reader box with the led light.

Any help in a new direction would be much appreciated.

um, afaik, *ALL* US model 940's have the blinky-box up to and includuing 1995, which was the final year of US sales. in 1996, the USA required all cars to have ODB-II, which would have required a fair bit of reengineering, and the 940's sales were flagging compared with the 850 new model.

now, if you're in another country my apologies, and I can't really help you there, as I have no idea what they did in your market.

btw, the reader box is over by the power steering reservoir and forward of the left fender strut tower, out of sight in your picture. it has a cover on it, so it just looks like a 1" or so flat black box. many later cars had a pair of them, A and B, mounted back to back.

It's a U.S. model
 

Pic is from yesterday. From your description it appears I have 2 of these. I'll take a look soon. Thanks

Air mass meter problem
 

That was kind of cool. Codes 322 and 121 were read. Both have to do with the air mass meter.

I thought I would locate it and take it off to inspect. A quick search tells me it's in the front of the fresh air hose on a 240. I'll go with that, if I need correcting please jump in..

I'd clear the codes and see if they come back after sorting out the idle symptom.

really, your occasional low idle suggests to me that the idle microswitch on the throttle sometimes doesn't engage... at least, thats the simplest single cause. the fact that the low idle is 400-500 suggests everything is adjusted correctly, other than that idle switch itself.

cleared codes
 

Well that was rewarding, I followed the directions and it worked. The code reading was kind of fun for us. I removed the air mass sensor/meter just downstream of the air box and cleaned the inside with contact cleaner. The electrical connections had light corrosion, they were also cleaned. I cleared the codes and the check engine light went away.


On my next visit I'll check the idle switch.


Thanks pierce!