rough cold starts and various DTC codes.

[dj747]

I have a 2001 sport track 4.0 SOHC with a DTC ( check engine light ) that likes to idle very rough when cold, almost to a stall. I pulled obd II codes and came up with p0171,p0174 bank 1 + 2 too lean the first time. I checked for vacuum leaks a didn't find any. I cleared the codes and DTC poped up again with same codes but this time included a p0300 multiple cylinder missfiring and p1506 low signal on iac. Is it possible that a bad idle air control valve can cause missfiring and the fuel system to be too lean??? I have checked the valve resistance and voltage and it reads fine, and all the other sensors related to the system are reading fine too. After the engine warms up it runs and idle very smoothly even though the check engine light remains on. what might be the problem? PLS HELP...
THANKYOU.

 

[toad]

Exactly the sme problem here, great if its warm, bad if its cold. If I leave the block heater plugged in and its fine also.

I have replaced IAC, checked for vaccum leaks, cleaned MAS, etc. etc, still loads up when cold, throwin codes 171 and 174 some times as well, no others though.

So ya, like you I dont know, the 90 deg. vaccum elbow sems to be it alot, but mine looks fine. Whats next??, O2 sensors?, intake gaskets? I dont know, soon it will be warm here and I wont know if its fixed anyway, lol.

Good luck, Todd

 

[Squirrelmaster]

Double check for vacuum leaks, in particular around the intake gasket. Also check the PCV for leaks and proper function (they're really cheap, so you might as well replace it). Next would be to check fuel pressure, as you may have a fuel pump beginning to die, or leaking injectors, or a bad fuel pressure regulator. You can also pull the plugs to double check the wear and gap (you can also read them for a lean and rich condition to verify whether the codes are active all the time or only at startup). I doubt it's an ignition problem you're having as you're getting lean codes instead of rich (P0172/0175), but it's still not bad to double check everything.

dj747 - My guess based on past experience would be check the fuel pressure regulator first, as I've had several bad FPRs on other vehicles that caused hard starts and misfires/lean conditions like yours. The IAC typically doesn't throw a code, and if it did it wouldn't normally throw these codes, but you can still clean it if you would like as that's not really a bad thing to do with the IACs on these trucks.

toad - Double check for vacuum leaks at the intake gaskets and PCV. I've seen a couple times where a cold block led to leaks which disappeared when the block warmed up (contraction and expansion of the various materials). Next check the fuel pressure, though I would tend to think this may not be a problem for you as a bad fuel pump usually shows up when warm (heat is the enemy to fuel pumps, as the gas is there to cool them), and a bad FPR tends to show up all of the time, though usually more so when warm as well.

Best of luck gentlemen.

Tom

 

[dj747]

well guys i really apreciate your advices and i will try everything i get that i havent done yet. now something interesting i found out today. i unpluged the coolant temperature sensor. this increased the fuel flow and rpms to about 850-900 rpm. defenetly making a big difference in the idle. much smoother. I havent got a chance to really troubleshoot the sensor since it is located in a hard to get area. I also found out that there is no intake air temperature sensor so the pcm uses the signal from the coolant temp sensor to adjust fuel during cold start. i will get more in to this i let you guy how it goes.

thanks!

 

[ttbit]

This is a common question that I see every time I get on the forum. It was the intake gaskets for me and most people that have these symptoms. VERY common. Pain in the butt job, but it can be done without special tools.

 

[dj747]

well i took apart the intake manifold and i found out that it wasnt seated properly, also one of the bolts was striped. I inspected it and found out that the manifold wasnt crack it was just the thread that got damaged. I put everything back together and it seems like the low iddle is gone. I would like to know what would be a normal initial iddle speed because now it seem to iddle pretty high until it warms up. once again thanks for the advice.

 

[toad]

Sounds good guys, Im thinking this is likely my problem as well, now I just need to find the time to rip the intake off, lol.

Todd

 

[ttbit]

Glad you got it fixed. I am surprised you didn't have to replace the O-ring gaskets though.

 

[ttbit]

Whoa.....resurrection. : ) 2008. Impressive. How time flies.