1998 Volvo V70 stops idling at 97 def F

[mattrector]

I am the proud new owner of a 98 V70 base with 117k miles. The car is in wonderful shape and was well taken care of by it's one owner. It starts right up and idles just fine until the outside temperature, according to the temperature on the dash. It had been dying on me whenever it was hot (outside) I would take my foot off the gas and it would die. Today my wife was driving on the freeway and it was running just fine until I saw the temp get up to 100 and you could feel it shudder and then when she took her foot off the gas and we slowed down it would start to stumble and would have died if she hadn't hit the gas a bit. We did the "feathering the pedal" trick until we got of the freeway and I noticed that the temp had dropped to 95, all of a sudden it was idling fine. We went through a couple of lights and everything was fine but as we got closer to home I noticed that the temp had risen to 97 degrees and the it started to stumble again. When thinking back this seems very consistent with previous behavior.
I have pulled and cleaned the IAC and fixed at least one vacuum leak with no change in behavior. It threw a PO171 code today as well. I just looked at the MAF and it might not be a Bosch (how could I tell?) but I haven't cleaned it. Any and all ideas would be much appreciated!

[wizechatmgr]

I think I'd replace any non-Bosch MAF before I even looked at anything further. Bosch MAFs almost always (if not always) have their brand name on the side.

[callahanoffroad]

Yeah, I agree with wize. Pull the electrical connection on the maf, see how it idles. You can also grab a can of maf cleaner at Walmart and clean it. If that fixes your issue then it's for sure the MAF.

Bosch should be stamped into the actual MAF housing. You remove it with the safety torx screws in the plastic housing.

[abscate]

MAF on a base is probably a DENSO. even better and more reliable than Bosch.

It’s still got a vacuum leak if you are getting that code.

Evaluate,the ignition side for wear, check the fuel pressure regulator for loose gas, and search threads on how to jump the fuelpump relay. These often go in hot weather on an intermittent fashion.

[erikv11]

Maf on a base is probably a DENSO. even better and more reliable than Bosch. ...

All of your other comments appear spot on as usual, but this one is not. Absolutely no Denso sensors on a 98, this 98 base needs a Bosch MAF (only).

[abscate]

Maf on a base is probably a DENSO. even better and more reliable than Bosch. ...

All of your other comments appear spot on as usual, but this one is not. Absolutely no Denso sensors on a 98, this 98 base needs a Bosch MAF (only).

Thanks Erik. So base cars went DENSO in 99 I guess ?

Humility is stupid leaving the brain.

Fixed above

[jreed]

This may be a long shot, but it might also be worth checking the condition of the engine coolant temperature sensor (ECT), wiring and connector.

[E Showell]

I'm with jreed on that one. Bad ECT can cause all sorts of hurt. Mine have usually showed up as hard starting, however.

[erikv11]

... So base cars went DENSO in 99 I guess ? ...

Affirmativo

And from the clever suggestions so far I would check in this order:
(1) MAF must be Bosch (If that's not giving you trouble now , it will soon, just remove it from the equation)
(2) fuel pump relay (when it gets hot resistance goes up, current goes down, not enough fuel)
(3) ECT

[jreed]

Agreed with the above. If those three items don't resolve the problem, and you've checked all the vacuum lines, o-rings, hoses and fittings and are sure there's no vacuum leak anywhere, it might be a good idea to try swapping out the IAC. A few (5-6) years ago, I had trouble with stalling and rough idle on my '97 and when I was cleaning the IAC I noticed that it didn't turn smoothly. I replaced the original IAC valve with one from the junkyard and the stalling and rough idle was eliminated... haven't had a problem since.