3L ATX Idle issue

[Blackcoog]

I swapped a ported 3L into a 1999 Cougar ATX. The engine setup is as follows:

-2005 3L Taurus with ported heads
-Porting plates installed with gasket sealant
-SVT lower intake
-19lb Mustang Orange EV1 injectors (plugs directly into the return harness)
-SVT upper intake
-SVT throttle body/cable/bracket
-BAT intake pipe with K&N filter
-MSDS headers
-Aftermarket Y pipe
-Stock Cougar single exhaust

The car started fine but it won't idle in park. I can give it gas to keep it going. I can put it in drive and that for the most part keeps it running except for the occasional stall at idle. It will drive fine. I had a CEL for the IAT sensor which I cleared and it hasn't returned. Sensor seems fine.

I have a Xcal 3 with a tune from Nautilus for the car which I loaded up but the idle issue is still present. Nothing changed with the tune.

I then tried swapping parts. I swapped the idle air controls sensor, MAF, and throttle body over from my car without any luck. I removed the upper/lower, verified the injectors were firing, and put it all back together carefully to check for any obvious signs of vacuum leaks. I didn't find anything and to me it doesn't seem like a vacuum leak issue. Usually you can hear a large leak. I noticed that when the MAF is unplugged the car will idle and run perfectly..... WTF? I thought I'd give the stock tune a try again but when I tried to load the stock tune back in (Xcal 3) it says "unlock ECU failed"...

Anyone have any suggestions/ideas/thoughts?

Thanks,
Chris

 

[Blackcoog]

Car will hold a rough idle when warm. I do think I'm hearing a hiss under the throttle body/PCV/IMRC linkage area. I pulled the upper again last night and I carefully looked at the upper intake for cracks. Nothing found. I carefully reinstalled and the hiss is still there. No check engine light but I ran the codes anyway and lean codes popped up so it's definately a vacuum leak. The brake even gets hard (loss of vacuum) when the revs drop (coming to a stop). Damn car. lol

I was able to put the stock tune back in. I'm not sure what my buddy was doing when he got the ECU error. Maybe the battery was a bit low.

My ideas so far are:
-Leak around porting plates (I guess I'll remove and reseal them tonight)
-Leak around LIM secondary shaft bearings (I guess I'll try another SVT lower and upper for that matter)
-PCV system leaking (I'll remove and check it over)

 

[crewchiefpro]

I would spray starting fluid where you think the hiss is coming from, it will either rev up or down if there is one.

Raise the Idle RPM with the XCal also once you are done. It is fairly easy to do.

 

[fogartyjohn]

I am going to agree with crewchief on this one man. How does the PVC valve look itself maybe try changing that sense it is only a few bucks. I used my xcal on my turbo car to raise and lower my idle. It is vary simple procedure.

 

[BrApple]

If the car runs better with the maf unplugged I would start there. Try swapping another one it and see what it does.

 

[Blackcoog]

Noted above MAF swap didn't change anything.

I fixed the issue last night. There was a slight leak around the throttle body gasket AND a leak around the PCV valve. Both relatively minor but since there were two leaks it was more of a pain to track down. Car runs great now. Thanks for the suggestions!

Unplugging the MAF must make the ECU switch over to a rich tune which kept the car running.