: Rough idle-stumble on accel

07-16-09, 09:11 PM
2004 SRX V8 Northstar (4.6L-LH2) AWD, 85K miles. Recently changed the plugs, removed & cleaned the TB, also have run a can of BG44K through the tank.

Am having idling/missing problems, and it stumbles when throttle is initially engaged...

I have access to a Tech 2 (am not proficient in its use)...Hooked it up and got these DTC's;

P0106; MAP/Barometric Pressure Circuit Range/Performance Problem
P0171; System Too Lean (Bank 1)
P0174; System Too Lean (Bank 2)
P0300; Random/Multiple Cylinder Misfire Detected
P0420; Catalyst System Efficiency Below Threshold (Bank 1)

I cleared the codes, and idled it for 5 or so minutes, no codes reappeared...

Also should mention that I hear a loud ticking from the engine (lifter, valvespring?)...

Any ideas? I did perform the Short term/long term fuel trim comparison, and for bank 1 all values were +8 to -8. For bank2, long term fuel trim was +10, and did not decrease when RPM's were raised to between 1500 & 2000 (if it did decrease, it would indicate a vacuum leak)..Seems to suggest a fuel restriction?


07-16-09, 09:15 PM
Is this a Northstar?

07-16-09, 09:18 PM
Sure is, 4.6L, LH2

07-16-09, 09:23 PM
Spray some Brakleen around the bottom of the plenum and listen for an RPM increase. The plenum is the rubber coupler between the TB and the intake manifold. They tend to rip on the bottom where it can't be seen and can cause the symptoms you are having.

07-16-09, 09:43 PM
I tried propane (using my torch). I ran it along the interface between the head and the IM, as well as by the TB, to no effect...

07-16-09, 09:48 PM
Might try cleaning the TB, but P0171 & P0174 indicate a vacuum leak somewhere.

07-16-09, 09:57 PM
I did clean the TB (mentioned it in the first post)..I do appreciate your help, by the way...

Any thought on the tech suggestion regarding raising the RPMS to above 1500 to see if the STFT/LTFT decreases from the 10+ value? The tech tip indicated that should the fuel trim value decrease during this high idle, it indicated that a vacuum leak was likely, however, in my case this did not happen (value stayed at 10)...

07-16-09, 10:13 PM
Nah, I'm at a loss on that one.

07-16-09, 10:28 PM
Deal with the MAP sensor first (your P0106), and go on from there. It may be just screwing up your fuel mixture. If not, then at least you got one of your problems fixed.

07-17-09, 07:48 AM
Should I replace the map sensor? I did try unplugging it, which had no effect on the "miss"...

07-20-09, 09:22 AM
Checked it out this weekend; the miss doesn't start till it is driven a short distance. If started and is idled only, it doesn't miss. Once driven, it starts to miss and does not stop, whether driving or idling. Also, it is a hard miss, in that, it's like the engine has nearly been shut off. It does so very quicly and abruptly...

07-20-09, 01:42 PM
The MAP sensor code could be from a bad MAP sensor, wiring problem, or a bad circuit in the PCM. You would need the diagnostic trouble tree for that code to figure it out before you buy anything. Otherwise, it's just a game of guess and check.

07-25-09, 11:52 PM
We found the problem. A co-worker hooked up the tech 2, and noticed that the misfire counter was reading a lot of misfire on #7...I bought a used bank of coils (nearly new, only 5 miles on them!) for $65, installed them and no more misfires....Seems all is well. I plan to clear the codes, drive it a bit tomorrow then see if there are more codes...

Thanks everyone for your help...