(IAC p1505 & p1507) 98 V70t5 Question

noev70t5 · Post by **noev70t5** » 20 Sep 2017, 12:53

Turned on like normal - Once it hit operating temp it started surging the idle and CEL while still in park

Ran the codes: p1505 p1507 - (Open and Close IAC)

Took one from the salvage from another turbo model and replaced my old one.
No problems - (Left my car on, in park, while I did my arrands right after replacement - No issues)

Seemed like it hiccuped and I assumed the IAC failed again as it started surging again and CEL is back with the same codes

Another replacement from the salvage and no luck. Still surging.

Ive disconnected my IAC and my car runs pretty damn close to normal with no surging or flutter on my vaccum gauge
In park it's right under 1000 RPM (slightly high) and in Drive, stopped, im at about 800 RPM (slightly low)

I dont know if theres another sensor thats making my IAC freak out?
(my O2 sensors are way overdue and every blue moon cause a CEL) Crank Angle Sensor maybe?
Or should I stop pulling IAC's from the yard and invest in a fresh one?
I can pay the dealer $170 to pinpoint or I could buy another IAC w/fresh Vacuum tree to IAC hose for $200

Any suggestions on where to start?

Thank you for any help!

noev70t5 · Post by **noev70t5** » 22 Sep 2017, 08:50

Interesting Update!

Ive been driving with my IAC disconnected for a few days. The one that's currently on there is the second one I got from the salvage.
Out of curiosity I decided to reconnect it to see how it reacted. I turned on my car while it was disconnected, after maybe 1 minute I popped the hood and reconnected my IAC. To my surprise it did not surge! Vacuum held nice and the idle was steady at 900. It threw me off because this is the same one that, when connected earlier, caused my idle to surge just like my first one.

I was eager whenever I pulled those other IACs from the yard and slapped them on while I was there. Did installing the part while the engine was warm have anything to do with it or should I be cautious about impending electrical faults?

noev70t5 · Post by **noev70t5** » 22 Sep 2017, 15:24

Put the car under 6lb of boost and it threw the IAC out of wack.

Im clueless

Post by **abscate** » 23 Sep 2017, 06:01

I'm wondering if you have a vacuum leak or induction leak that shows up under boost

Time to take them all off, clean , and look for splits. You can't check these while they are in the car installed

noev70t5 · Post by **noev70t5** » 23 Sep 2017, 12:35

In an attempt to be extra careful Ive been taking off all hoses when replacing the IACs - and everything seems ok except the hose at the top of the vacuum tree.

A new hose was put in the order with my new IAC so theyll arrive at the same time. I think im going to change my o2 sensors at the same time (No record of the last time they were replaced nor have I done it in the almost two years ive had the car)

This morning I did the same thing: cold start then immediately pop the hood and reconnect and everything was good. Got to operating temp and it was still fine. I drove 45 min into downtown and whenever I let off the throttle at 60-70 mph my boost gauge started the flutter again around 20-22 InHG on the vacuum side and CEL followed.

If the new part is still reacting bad im taking it to the dealer for a good inspection. Im going to keep this updated regardless of response for anyone else who goes through this. Ive read a few posts but no one responded nor did the original poster post the solution

Thanks for any input!

noev70t5 · Post by **noev70t5** » 08 Oct 2017, 06:15

Well I replaced my IAC with a new Bosch brand IAC and I am STILL experiencing a surging idle when the IAC is connected. When I first installed the new one it ran pretty well for about a week and a half. Then the surging began again. It surges and sounds like its trying to suck air through the vacuum tree. While its surging the noise and the vibration is coming from the intake manifold not my intake filter so I don't understand the suction attempt noise as if its trying to create a certain vacuum

For the sake of not having the vacuum fluctuate rapidly I have been driving without my IAC connected.

Where should I go from here?

No one else seems to be asking p80 IAC questions (and when they do even on other forums there is almost never a response)

Post by **abscate** » 08 Oct 2017, 07:17

The noise is from the surging, no the other way around. As the revs fluctuate, the air charge moves back and forth in the manifold and thus you hear strange noises as the engine sucks air in as it stumbles back to good revs.

Put a vacuum gauge on it, check induction path and finally smoke it to find a hard to find leak

Post by **erikv11** » 08 Oct 2017, 07:55

IAC problems are uncommon. Usually just cleaning it works fine. Engine surging problems, however, are common. Induction leak seems mostly likely, as abscate suggested.

When you say "driving without IAC connected" are you driving with the lines to the IAC actually disconnected, or do you mean you unplugged the power to the IAC?

noev70t5 · Post by **noev70t5** » 08 Oct 2017, 13:07

With that p80 poll going on I agree, it apparently is not common at all.

Without it being plugged in is what I meant, the hoses are still on.

Has the intake manifold gasket ever caused an issue similar to this? Im sure my gasket is toast by now.

If it is an induction leak should I check all vacuum hoses or is there more to it? Cause ive noticed a bit of fuel getting past my injectors onto my intake manifold which hasnt been there in the year and a half ive owned the car.

Post by **abscate** » 08 Oct 2017, 13:39

If your injectors are leaking fuel out onto the manifold that will cause bad running. Fuel leaking out also means air leaking in.

The ECU received data from the MAF telling how much air is going into the engine. THE ECU then sends the right amount of fuel. Any excess air that leak in will mess up the idling and low rpm running.

Checking induction is about 2 hours of removing, inspecting and reclaiming the hoses from MAF to the intake manifold.