Cleaned the idle air crontrol valve, and unplugged and cleaned every connector I could find under the hood, a couple were pretty green so I thought for sure that would have fixed it. It didn't. Then I changed the FPR, it's needed it (long cranking time) for a while. No joy. Found a few rotten vacuum lines which I replaced. No difference.

Car is a 2001 S40 with only 115k miles on it. Runs fine, drives fine, but you have to rest your foot on the gas pedal to start the engine and to keep the engine from quitting when you come to a stop.

I'm not getting any codes from any of this.

Could a mass airflow sensor fail without throwing a code?

I need to go in a new direction here, not sure what to try next but getting extremely frustrated. That's for any ideas.

 

Check to see if there is any buildup of gunk around the throttle plate. The throttle plate is designed to let a small amount of air to pass around it when closed so the engine will idle. If too much dust/oil gets gunked up around the throttle plate it can seal it off and the engine will not idle unless you open it slightly.

Pull the large intake hose off and open the throttle by hand (with the engine off of course!) Reach in with a finger and feel for a slight ridge where the plate sits in its closed position.

I had this happen on my Focus and ran it with a small peice of paper taped on to hold the throttle open a hair. Took me a month to figure out what the real problem was!

 

I had the same thing happen to my ford esacpe,,,also would not idle...it was the idle air control valve....I cleaned it...did not help and eventually relaced it with new one and that did the trick...you might need a new one

 

Will try those things.

Can you take the IAC valve off and leave it plugged in, turn the ignition on, and see if the valve moves? Is there a way to troubleshoot?

Also want to mention that I just went out and unplugged the MAF, and let the car run for about 5 minutes. The STC warning light did come on, but the CEL did not, and still did not throw any codes which I checked with my code reader after shutting the engine off. No codes even with the MAF unplugged? Also ran exactly the same, which is to say pretty good except for the idle. Did not drive it.

I just want to be sure before I go ordering expensive parts.

Heck, this could be the TB, MAF, TPS, manifold pressure sensor, or another vacuum leak I haven't found yet. It could even be the ECU. Very hard to troubleshoot exactly.

 

Well I plugged my scan tool in and ran the engine while monitoring all the parameters, and it seems everything I can see is working. It gives data for throttle position, Manifold air pressure, Mass Air, a bunch of other stuff, and no data fields are blank. I assume I can safely say it is the IAC valve then? Any comments on this before I plunk down the money?

 

The old school test for the IAC is to remove it with the engine cold. Now hold the IAC in one hand while placing your other thumb over the large square hole. Have an assistant start the car while you regulate airflow with your thumb. As you vary idle speed you can watch the IAC pintle for movement. You will need a replacement gasket if you remove the IAC as the original will most likely be destroyed on removal.

While you are in there check the S shaped hose that connects the air/air intercooler to just below the IAC. Mine cracked in two and caused some idle issues.

 

FYI guys it was indeed a failed IAC valve, I got a new one off Amazon of all places and swapped it out, now all is good, with that and the new FPR it starts better than it has in years.

 

Hi, I've just been roaming around this site for a day or two looking to fix my daughters 2004 S40 1.9T issue of "won't idle"

CORRECTION: It was a fuse, but it was the 10A ENGINE SENSORS fuse, NOT the 15A Fuel Pump fuse.

The fault code signature I got when re-installing the 'Bad" fuse were: P2401 P0445 P0031 P0037 P0245

Can't believe it myself, but it was a FUSE! I can duplicate the problem by swapping the "bad" 10A ENGINE SENSORS fuse . I triple checked it. Also, when this fuse was put into the POSITION LAMPS slot I got no rear lights at all, again, this fuse ohms out!?

To be clear here was the cars' issues:
Symptom: Starts but does not idle; runs fine with foot operating the throttle, but stalls immediately if you remove foot.
Originally it ran for a week after purchasing car, then the problem appeared intermittently, 2-3 times in one week – wouldn’t idle upon start-up but then ran fine after it was run/warm for several minutes. THEN, a few days later, it became a HARD FAILURE, constant all the time will die without operating the throttle. FYI; OTHER odd note, the FAN coming on even when cold.

ACTIONs TAKEN:
1) Removed and cleaned ICV (idle control valve)
2) Bought and installed brand new ICV
3) Ordered an OBDii reader to get codes (but from other posts here I don’t see this leading to resolve)
4) bought STARTER FLUID to go hunting for vacuum leaks. Nothing obvious found (person in car kept a steady idle as I sprayed starter fluid over vacuum hoses and all around).

FINAL SOLUTION:
Read that a Fuel Pressure Regulator solved on guys similar if not exact issue according to his description. So not wanting to spend $140 to find out, I wanted to use a Fuel Pressure Gauge to simply measure the pressure - but in one day could not find one to borrow. So I did a lazy man and depressed the Schroeder valve on the test port and fuel spewed out. Not sure if the pressure was adequate but also because the car ran fine operating the foot throttle also seems to indicate to me that the fuel is being delivered just fine. So then I thought to at least check the FUSE - it looked weird somehow in the loop arch, couldn't tell if it was blown, ohm'd out using a DVM and it rang the continuity beeper. Also the leads were discolored, but all my fuses are discolored. side note: Previously I had a Cruise Control issue not working that seemed to be fixed by cleaning the tarnished leads on the FUSE. So I cleaned the leads on the 10A Fuel Pump fuse and re-inserted it. - No change. I did the same to a few other fuses (10A Engine Sensors ? , 15A VACUUM PUMP), and each time went to start the car. - No change. Then I swapped out the 10A ENGINE SENSORS Fuse with another 10A fuse, and the CAR STARTED AND IDLED with no foot operation of the throttle pedal. I was able to swap the "bad" fuse back and the car would not start, swapped it again with the other 10A fuse and the car would start.

 

That has to be the strangest one I've read yet. Good job finding the cause.

If you are near a harbor Freight you can pick up a Fuel Pump Injection Tester for $20 or so. It's a cheapy Chinese unit but it gets the job done for us DIYers.

 

Hudini, thanks. I thought I'd get someone to comment in that regards, it is very strange! I intend to duplicate the problem AGAIN, just cause I still don't believe it. But I did each scenario the first time, 3 times each: that is, with "bad" fuse I attempted to start it 3 times in a row without any foot throttle, it would not start. Then I installed the 'good' fuse and attempted to start it 3 times in a row, car started right up and idled fine each time. Then put the bad fuse in for a final time and it would not start. I should be convinced. but its so strange, cause the fuse ohms out to near zero resistance and the beeper goes off. But I will triple check and also shoot a picture of the fuse and post it here. Its so frustrating to read posts that just end and do not have root cause solutions posted - that is a complete waste of this whole forum. I think administrators ought to DELETE old posts that have NO SOLUTION. so members don't waste time reading.

Hope you saw I updated with a correction:
CORRECTION: It was a fuse, but it was the 10A ENGINE SENSORS fuse, NOT the 15A Fuel Pump fuse.
The fault code signature I got when re-installing the 'Bad" fuse were: P2401 P0445 P0031 P0037 P0245

ps. how do you know of Harbor Freight if you are in Shanghai?

 

I only work here. I'm from Knoxville, TN. We only have one little Harbor Freight there. The funny thing is I can probably buy the tester at the source here and it would cost much more. The Chinese tax anything made here that is also sold here. If it leaves the country then there is no tax.

 

Compliments Junior Member.
I have a V40 2.0 T - 2001 km 212800.
after a lot of money spent at Volvo to solve the same problem you explained, changed some parts of the engine, lambda included, without to solve my car’s problems, I finally arrived to this solution by your clever job. Probably nobody, in Volvo official repairers is able to arrive to this so easy solution because either the Volvo Official Service and Repair manual is not indicating your solution: THE FUSE n18 of Engine Components.

Thank you so much and compliments.