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Volvo V40 won't idle (sometimes)

We have an 04 Volvo V40 which won’t idle when it’s cold out, especially at altitude. Not all the time- it seems to be somewhat random, but it is getting more frequent. Our mechanic has replaced the MAP and TCV sensors and that didn’t make any difference. Any thoughts on what to try next? It recently passed an emissions test, so when it idles, it runs fine.

Why did your mechanics replace those parts? Guessing? Is the check engine light on and were error codes read? If so then report the exact codes (format: P0123).

If there are no codes, the first thing I would have done is clean the throttle body, idle air control valve (as I think the '04 V40 still had one), and the MAF sensor. This would have included a check of the wiring for the IACV and MAF.

I agree with @cigroller‌

Replacing the MAP doesn’t make any sense. That was just a wild and crazy guess, I think.

Cleaning the throttle and IAC often works wonders.

One of my cars had an unsteady idle, and would stumble. I cleaned the throttle and IAC, and all is back to normal. Cost me just the can of carb cleaner.

A general tune-up (including reading any diagnostic trouble codes) and those items mentioned above would be a good place to start. I suppose the reason they changed out the MAP was b/c of the altitude-related symptom. The MAP is critical to how the ECM determines the altitude adjustment for air/fuel mixture. A MAP should be easy to test though. While it might be removed for bench testing, it usually it wouldn’t be replaced with a new one unless the bench test showed the calibration off. Since the symptom remains it must not have been the MAP. Maybe you can get your old one back, and the shop can sell that one to somebody who actually needs a new one.

hmm … what else? … Only happens when outside temp is cold, even if the engine is warmed up? Well, there’s probably and intake air temp (IAT) sensor. Likewise there is probably an engine coolant temp sensor. No harm to test both of those. Vacuum leaks could cause a cold-related idle symptom too. Mechanics know how to test for those. The first vacuum leak suspect would probably be a leaking diaphragm in the brake booster.

Actually they replaced the MAP since that was the error code they picked up. They have also replaced the IAC. They haven’t charged me anything since they haven’t been able to fix it yet. I’ll ask if they’ve checked the wiring to the IACV too. Everything they have checked on the fuel side has been clean- I run engine cleaner (Seafoam) thru the engine fairly regularly since the car only gets driven by my daughter on very short trips. Since we now have to drive it w/ 2 feet, my husband is having to drive it and he’s not too pleased.

“Vacuum leaks could cause a cold-related idle symptom too.”

Agree. Also, look carefully at air hose between MAF sensor and throttle body for cracks.

There isn’t “a” code that can tell you to replace the MAP sensor:
P0068 MAP/MAF - Throttle Position Correlation
P0069 Manifold Absolute Pressure - Barometric Pressure Correlation
P0105 Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
P0106 Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem
P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High Input
P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

Those are the generic codes that would “name” the MAP sensor. None of them tell you that the sensor is bad. In addition, there are probably also Volvo specific codes.

That’s why I asked what the exact code was. It can matter.

Were/was there also (a) code(s) for the TCV? If so, what?

Was the MAF cleaned? The throttle body?