My idle issue involved the idle not being at 750 RPMs at idle in gear. It would idle at around 600 RPMs. I believed my IAC valve was going bad so I gave it a cleaning a couple months ago (by unloading 1/2 can of TB cleaner into it). It didn't solve the issue so I bought an used, but cleaned IAC valve on eBay. This replacement IAC didn't solve the issue. It did make the idle jump up and down (it'd go up to 750 RPMs and drop to 550 RPMs and repeat) when cold and it idled roughly when warmed up.

I cleaned the original IAC some more with the remaining can of TB cleaner (and used electrical contact cleaner on the wiring harness) and I noticed that now when I sprayed in the hole at the end it was dripping TB cleaner out the hole that points downwards. It didn't drip on the replacement IAC and it didn't drip the last time I cleaned the original IAC.

So my questions are:

1. It seems like after noticing the drippage and reinstalling the original IAC the idle improved slightly (still lower than 750, but doesn't idle roughly like the one I bought off eBay. Is the IAC valve naturally in the open state when not powered?

2. Would you say the replacement IAC I bought is defective? The seller claims that the issue I'm having is not an IAC valve problem and won't do an RMA.

 

if the car is LH2.4 (1989+ non-turbo and 1990+ turbo), it has the OBD diag box, there's a DTM3 on jumper 2 that will cycle various actuators on/off/on/off, including the IAC. disconnect the rubber hose, and connect a clean piece of rubber hose, and blow gently through it, and you should feel your breath chop on/off/on/off (this test will also cycle the fuel injectors, electric fans, and so forth).

make sure the throttle body is clean and is closing completly. make sure the idle switch on the throttle body is closing when the throttle is at idle. make sure there's no vacuum or air leaks in the intake path between the MAF and engine.

 

First I would go through the cleaning process of the TB and IAC making sure you don't get the plastic and electronics wet with cleaner. Then I would reset the throttle stop screw to idle without the IAC connected at 500 RPM. Then reset the TPS and check all of the intake tubing for leaks. Hook everything back up and start it up. Now what do you have for idle speed and smoothness. I assume the plugs are clean and not fouled and the ignition system is in good working condition.

 

if you set the idle speed when not in gear at 750, it will be slightly lower than that when youre in gear. there is a spinning mass slowing down the rpms. Just saying...

Also you can adjust you idle screw for 800 and it will work better.

 

cranking the idle screw up above the level it tries to regulate at effectively bypasses the regulation.

 

It's a '92 940 2.3L w/ Regina FI. I snapped the throttle rest screw when I adjusted it. The screw came loose and it caused the throttle rest sensor to think it's never at rest causing it to idle high and slam into gear when moved out of park. I adjusted the screw back down using pliers and loctite'd it in place and it's the same as before I fkd with it.

Spark plugs, distributor cap/rotor, and wires are all new. I found a receipt for TB servicing in the car dated Feb 2013 so I assume that the previous owner had it cleaned. I wiped down what I could get to without taking the TB off and it didn't seem too dirty. Acceleration is great with no hiccups and it doesn't feel wrong. I do plan on changing the fuel filter soon.

Pierce, can you tell me more about this DTM3/jumper 2 thing? Where is this jumper located? Where is the OBD box?

 

Engine and OBD Diagnostic Codes

 

Somehow I don't think you got the idle adjustment correct. I would suggest you replace the damaged screw and adjust the idle by the book with the IAC disconnected and plugged. Once you do that you can adjust the TPS and it should go to normal idle as long as your water temperature sensor is working correctly. Go back to the basics and then see if the problem is corrected.

 

Having idle fluctuations myself with an '89 740.

Pulled the IAC and used TB cleaner on it and the TB today. Also sprayed some TB cleaner into the TB through one of the hose ports while revving it by hand (DOWNSTREAM from the MAF).

It helped but didn't fix it (still occasionally stalls out unless you keep light pressure on the throttle, easier to 'catch' it before it stalls with the throttle).

The valve had some scoring on it visible from the bottom. Thinking now I should just bight the bullet and get a new one.

 

In case you decide to replace the IAC, this place seems to have the best price VOLVO Parts and Accessoires. VOLVO Parts for VOLVO repair and VOLVO Performance upgrade! www.VLVworld.com sells New and Used VOLVO parts for 240, 850, 740, 760, 940, S70, V70, S40, V40, S80, 140, 122, 164 and More

 

With the IAC hose disconnected and plugged what is your idle rpm. It should be around 500 RPM.

 

It died when I did that, so RPM = 0.

Replaced the IAC so idle problem mostly fixed, it doesn't die at stops now, but it does fluctuate from 500-1000 rpm. I disconnected the battery to clean the ground and terminals, so perhaps the computer is relearning.

 

When you pull the IAC hose off you need to plug the IAC hose and the hole in the main air intake hose. You then loosen the lock nut on the throttle adjustment screw. Try to start the engine and if it doesn't start turn the throttle adjustment screw in a quarter turn and try again. It should start and if not turn it another quarter turn . When you finally get it running set the idle at 500RPM and lock the lock nut down. You may or may not now need to adjust the TPS if so do it. Connect the IAC hose again and start it up. It should run at around 750 RPM at idle.

 

don't disconnect the IAC hoses, unplug the electrical connector to the IAC to set the static idle to 500. unplugged, the IAC should be 'closed', when it gets pulses from the ECU, it lets extra air in bypassing the throttle body, so it can only raise the idle speed, not lower it. the ECU will try and get the idle to a steady 750rpm once the engine is warm (a cold engine, it pushes up to 900rpm or so).

 

Should have mentioned the idle fluctuation is intermittent, most of the time it's at 700.

Also, the IAC is new and the set screw is fixed in place with epoxy, I am loath to mess with that unless it's a last resort.

I also replaced the flame trap, the hose underneath which I initially hadn't pushed into what I believe should be the oil separator. It ran poorly (wouldn't rev high) until I did that. Did not remove/clean the oil separator as the old flame trap was pretty clean and it was cold and raining here in NH (will do that in the Spring).

I also disconnected the battery for about 20 min to clean the battery ground, terminals, and connectors (they were really crudded up). Possible that the computer is relearning after having been disconnected?

TIA. You guys are awesome. Look forward to converting these to some modern engine at some point, or doing an electric conversion.

 

Pulling the plug on the IAC is OK too as long as we assume that it is closed and not leaking. As for the throttle adjustment screw if it is epoxied then you have a problem if it will not idle at 500RPM. That is why the screw is there to set base idle. look here Engine: Fuel Injection

 

For whatever reason, on a VW forum, people caution against using carb/TB cleaners on IAC valves and suggest using wd40. Don't know why, that's just the word.

 

I would assume that with WD40 it will not affect the plastic parts if you get carried away in cleaning. When using carb cleaner or brake cleaner you want to avoid getting it into the plastic and electrical parts of the assembly.

 

Probably because the WD40 leaves some lubricant behind, otherwise it's a dry valve.

I thought after I attempted cleaning my old IAC that I should spray some lube in there (not a fan for WD40 except for cleaning) as I had noticed some scoring on the valve. Instead I replaced it. Plan on taking my old one apart to check it out, maybe these can be disassembled, lubed, and put back into service.

 

Thanks for the link, I'm suspecting I have some sort of vacuum leak now (I also replaced the flame trap and fiddled with the tube going down to the oil separator in the process).

This is a bit strange: Replaced IAC/flame trap/plugs/wires/cap/rotor/air filter, cleaned TB and intake hose (did not mess with the air sensor, don't have the proper cleaner for it yet), checked/repaired every connection/ground that was obvious.

Air flow sensor says BOSCH, it's an '89 N/A.

My brick now idles rock steady at ~700RPM on start up, after driving it for awhile the idle starts to bounce between 200-1000.

At this point, if you rev the engine to 5-6000, it takes an abnormally long time to return to the (bouncing) idle, and it does so by idling down to ~4000, hesitating there, then ~3000, hesitates again, ~2000, etc.

Hopefully this will help solve the original poster's problem as well (not wanting to threadjack).