Hello everyone,
I just recently bought a 85 Volvo 240, and am have issues with the idle and emissions. My idle was high, about 1200rpm when warmed up, and I failed my smog for high NOX (California). I'm thinking the engine is running too lean, which is causing it to fail this test. When I start the car in the cold, it idles about 800rpm, where it should be, but as it warms up and I drive it, the idle goes up to about 1200. I checked for vaccum leaks, and sprayed starter fluid around the hoses, didn't seem to change anything. I believe my IAC is bad, and I pulled it, and it didn't pass the continuity test. When I grounded the IAC, there was no change in idle. Just wanted to know if I was on the right track for fixing this problem, in that bringing the idle down would solve the high "combustion temp". My idle was also surging a small amount, maybe 50rpm up and down, but the car still ran pretty good, and drives great. I'm also planning to change O2 sensor, as I know that can help to pass emissions.

 

The idle speed is controlled by the amount of air passing through the throttle plate plus whatever goes past the Iac/idle motor/whatever you want to call it. (an any other unplanned air leaks)

Earlier Volvos did not have an idle motor. Idle speed was simply what got past the throttle plate plus the manual adjustment screw. So - use spray carb cleaner to clean the inside of the throttle plate completely, easiest if off the engine but a new gasket is highly recommended. Then once the engine is warm - block off a hose to the idle motor (i always used a clamp - but that will probably crush and break an original idle motor hose today!) or some cars have a test point to ground that will allegedly set the iac/idle motor is a stable position. Set the throttle plate to have the car idle @ 750- 800 rpms. Set the throttle switch to click when throttle plate is moved off the idle position. This is supposed to tell the idle motor to try to maintain 750 rpms with your foot off the gas. Release the clamp. The idle speed should stay the same. And if the idle motor is working the idle should raise slightly when cold, when the ac is on, and remain stable when other loads such as the power steering or alternator are trying to slow the engine down. As mentioned earlier - you really don't need an idle motor/iac. if you can live with a lower idle when cold or other circumstances. you can adjust around (raise the base idle speed up to 900 or so) to not need a working idle motor.

Spendin money on an IAC is not going to fix your NOX problem.

Your NOX problem - 99% of those cars I solved high nox problems on were fixed with a new catalytic converter. There were many cars that had to have a new aftermarket converter every year - to pass emissions. (Few were willing to purchase a Volvo converter) In other words - don't plan on your new aftermarket converter solving the problem for very long.

Certainly "stage 1" would be the first step for any emission problem (good ignition parts, adjusted valves, no air leaks, etc)

It's certainly possible a 39 year old car could be running lean - and causing high NOX. Old injectors, low fuel pressure, carbon deposits on the back of the intake valves soaking in the injector spray causing a lean condition, intake manifold gasket leaks, air mass meter 38 years old - Take your pick - check as much as you can and start with the relatively easy stuff first.

 

thank you for your response,
I did ground out the point, and it didn't seem to do anything to change the idle, however, the engine was not warm I had just started it, but I did test the resistance using the end points of the IAC, and it didn't register any ohms, which I assume the motor is bad. I am really trying to avoid putting a new cat in, I know it would solve my problem right away, but funds are not there right now lol. I think I will change the plugs/wires/o2 sensor, run the **** out of it, and hope it passes . The car passed in 2020, so the cat probably just kicked it.

 

the IAC will vibrate when running so a quick test is to apply power and listen or simply feel it when the car is running. Also for the NOX problem, the easy path is to start looking for air leaks. Simple things like injector seals are probably old and crusty but can easily be replaced. You may need a smoke test to find bad vacuum lines or cracks in the boots. I think you plan should also consider how close you are to passing...

 

I did use the starter fluid test, and sprayed all around the manifold, boots, line, ect. and it didnt raise the RPMs, but I know it's an old car so I wouldn't be surprised if I missed it. The NOX was about 4-5x what it should be which is not that great, however my friend had his about 10x what it should be, and he replaced o2 sensor, plugs/wires, and he managed to pass. I think that the issues aren't exactly related, and I have 2 different problems to solve.

 

I've never used starter fluid (ether) to check for air leaks. I would think you would want something that did not burn easily - I've always used carb cleaner. Brake cleaner should not be used - some formulations produce a toxic gas when burned.

 

I replaced the IAC today, seems to idle better but still a bit high. After driving it around it idles 1k rpm. When I ground the lead out, it goes down to what it should be around 700-800rpm. I'm going to clean the throttle body next, but not sure what else to look at.

 

????? That should have been your FIRST STEP! But it's your $$ - so go for it.

 

Today I headed to my friends house and had him help me with the car. Cleaned the throttle body and MAF, changed intake gasket, coolant temp sensor, O2 sensor and some vaccum lines hidden on the bottom were a little cracked, so we fixed those. The o2 sensor was like white on the tip, and the plugs looked fairly whiteish too, so the car must be running lean. However, when we started it up, it idled higher than it did before lol. We shut it off, messed with the screw and looked at some stuff, and when we went to start it back up, it wouldn't go. Fuel pump relay was clicking, but we couldn't hear the pump running. but we were getting gas at the main line up top, and managed to get the car started. It was misfiring, then fixed itself, and I drove it home ASAP lol before i shut off again. Now it won't start up again. Any idea what we may have messed up on?

 

quick bump, I found the problem to be the coolant temp sensor we just replaced, the car would start after cranking for about 15 seconds. I guess the aftermarket ones from IPD don't work very well. Recently, I put the old temp sensor as it wasn't bad, just replaced it because my friend said so, and that it helped him pass smog. I'm back to square one with this idle issue though, I still believe it's related to the high NOX, since my CO and HP levels are low. In fact, the CO2 measured at 0.0, which i read indicated lean. I replaced all the gaskets, and checked for vacuum leaks everywhere and it all seems in order. New IAC put on that seems to be working as well. Not sure where my problem is however, maybe the mixture screw on the MAF could help ? or maybe the old coolant temp sensor is only half working. Could use some advice to help with this, thanks.
EDIT: also the flame trap is quite clogged up, not sure if that affects this, but I plan to switch that out.