Hi everyone,

I have a 1985 245 DL that I just purchased and I can't get it to pass CA smog. I am and auto upholsterer and know little about the mechanicals of an engine. I'm having idling issues, it seems to be running high, as i'm am told. My car does not have a tachometer, is there any other way to check my engine's RPMs? I have checked for vacuum leaks thoroughly and I have also cleaned the PCV, throttle body, checked for TPS alignment clicks, have the black idle speed screw in as much as I can turn by hand, closed off one of the idle air control valve and the engine wants to stall. Also I ran power to the idle air control valve and it does open and shut.

I've read some were that the engine should should rev up then rev back down shifting from drive to park, mine does not do this. When my car is in park the engine stays in the higher rev range and does not rev back down. I have also disconnected the idle air control plug started the car up and it sounds the same with it plugged in. Is this a problem?

Could there be a problem with my TB TPS? I have already checked for alignment issues and listened for the clicks. Does the TPS have anything to do with the IAC? Does the A/C effect idle? If so how do I check that it's not running? When I turn off the car I can hear pressure releasing behind the dash.

What else should I be looking for?

Thanks in advance,

David

 

with the idle air control valve disconnected, AND the idle hoses pinched off, your engine shoudl be idling at a slow speed of like 500RPM in neutral with all accessories turned off.

normally, when the idle switch on the throttle is closed, then the ECU monitors the engine RPM and tweaks the idle air controller to bring that idle up to about 700rpm (even higher when the engine is cold), and it should maintain that speed even with the a/c kicks in, or you put it in park.

my guess is, someone played with the idle screws to bring it up high enough to keep ti from stalling, and left it all messed up.

bunch of stuff you can test here. https://www.volvoclub.org.uk/faq/Eng...eSymptoms.html

note that just because you hear that idle switch click doesn't mean its actually making connection, you should confirm it with a digital multimeter.

 

Yes, not sure if all accessories are off though, how do I know if the A/C is on or off if I suspect the A/C switch is not working? I get a hiss, when I shut off the car and a hiss when I step on the gas hard. Is that sound my heater coil or A/C system?

How would I do this?

 

unplug the TPS, put the multimeter in 'ohms' mode, connect it to the correct 2 pins of the switch, and at idle, it should be 0 ohms, as soon as you move the throttle off idle so it clicks it should go to 'open circuit' (infinite ohms, my meter shows 0L in this mode). I believe the idle switch is the top pin, the middle pin is ground.... I generally use a pair of alligator clipleads for making this sort of connection instead of trying to jam my meter probes into the connector and hold them steady.

 

Would the mass air flow sensor effect idle? I have not check that out yet. How would I go about checking my mass air flow sensor?

 

Do I leave the car on or off when I perform this check? also how do I check the connection of the wires to the IAC? I have already ran 12v through the IAC and confirmed that it does open and close. It has been said many times that these cars have bad wires. At this time a new or rebuilt wiring harness is out of my car's budget. If my wires are going bad what are my options.

If the TPS is left unconnected when the car is running how will that effect the idle or whatever.

 

without the TPS, the control unit doesn't know your engine is supposed to be idling. I suspect someone twisted the air screw far enough to keep it from stalling, which is why your idle is so high.

my 'ohms' test above can/should be done with car switched off, you're just testing for switch continuity.

if you want to test the TPS 'through' the wiring harness, you'd go to the ECU, which is on the right side of the passenger foot well, just forward of the door hinge, and behind the plastic liner panel... unplug the ECU (ENGINE OFF!!!), and on the harness connector, locate pin 12, and test the continuity (resistance) from pin 12 to ground. throttle at idle, should be 0 ohms, off idle should be open circuit.

MAF is fairly hard to test. probably the best way to test it is to find another LH2.2 car (1985-1988 240 or 740) that runs correctly, and swap the MAF's... if the symptoms move to the other car, and yours is now working fine, good chance its your MAF. careful about replacement MAF's, there's a lot of junk rebuilt ones out there which are unreliable. a quality Bosch rebuilt one from a reliable vendor like IPDusa, FCPeuro, would be your best bet. you need a -007 MAF/AMM, later LH2.4 cars have a -016 which is NOT compatible.

 

when I followed these directions: Engine Tune and Performance:

"There is a blue connector behind the battery with nothing plugged into it . There should be a blue/white wire in the connector. Ground this wire it shuts off the idle speed motor so that base idle can be adjusted with the black **** on the throttle housing. Base idle for this car should be 700 rpm. When the ground lead is disconnected the idle should go up to 750rpm's +/- 20 rpm's."

I just jammed a probe into the blue/white wire and grounded it to the "-" on the battery terminal and nothing happened... tried it a few times and nothing happened...

What now? I've already checked the IAC valve with 12v and it opens and closes. I stuck an ohms meter on the IAC plug and I get some readings but I'm not sure what they it all means. Should I also ohms meter the IAC valve itself? Also if the IAC is unplugged when the car is running nothing happens.

David

 

air leaks on the IAC hoses, or between the throttle body, intake manifold, and head, will cause an excessively high idle. a gummed up throttle thats not completely closing will cause an excessively high idle. a mal-adjusted throttle thats not completely closing will cause an excessively high idle.

if the idle is too high there's nothing the IAC can do. it RAISES the idle from too LOW, so the goal is to adjust the throttle air bypass screw /without/ the IAC involved to idle slightly too low, like 700RPM when its fully warmed up, in park, with no accessories turned on.

btw, if you don't have a tachometer, you can connect a meter that has a 'Hz' frequency mode to the '1' terminal of the ignition coil and ground... the coil is fired twice per turn, and there's 60 seconds per minute, so multiply the Hz reading by 30 to get the RPM... 700 RPM should read 23.3Hz, 750 RPM would be 25Hz, etc.