HESITATION - 96 cobra

[Mystic1350]

hey guys, please help me out
my 96 cobra just recently started hesitating real bad around 2,300 to 2,700 RPM. it putters until past 2,700 then seems to drive fine. I also believe I have a small header exhaust leak.
I have read previous threads stating to change wires, plugs and clean MAF and IMRC..I just recently had the engine rebuilt so there are new plugs (not sure which ones they used) and they cleaned the IMRC and MAF. Also, i previously got ford racing plugs that are about 2 years old.

any ideas on what else could be this problem? It just started recently doing this approximately 3 days ago and previoulsy was driving fine since rebuild and LT/ H pipe installation .

Please help!
tkns

 

[mustang_jr+]

If you bog below 3200, imrc. It would throw a code too.

How steady is the idle?

 

[Mystic1350]

What would cause the IMRC to suddenly stop working? There have been no codes for this as well.
Idle is kind of rocky in neutral-flucuates between 800-1300 and then before coming to a stop it revs at like 1500 then back down. i dunnoo
any thoughts?

 

[mustang_jr+]

What would cause the IMRC to suddenly stop working? There have been no codes for this as well.
Idle is kind of rocky in neutral-flucuates between 800-1300 and then before coming to a stop it revs at like 1500 then back down. i dunnoo
any thoughts?

If the idle is rocky first thing I would replace is the IAC, and clean the MAF. I had to do the same thing on my car, I used to get fluctuations. Changing the IAC did it.

If the IMRC was stuck you'd just have crap power, it would feel like
you were towing a boat. The imrc actuator can break apart inside the module,mine were only stuck from oil ( I put in an oil separator because the emissions dumps the oil vapors into the intake, gumming up the imrc) A can of seafoam fixed it.

 

[Mystic1350]

What is the IAC and where can i find it in my car? is this something i can get at local auto store? Also, what is best way to clean MAF? I will try seafoam....hopefully this will fix the bogging below 3250 rpm

mustang jr--sorry about what happend to your car man.. you got pics you can send of the acetone and what it did to ur car?

 

[Mystic1350]

mustang jr--i just found out what the IAC is and i actually replaced it about 2 years ago, however the car sat around forever so maybe it got dirty?

 

[SVT32VDOHC]

Sounds like the IMRC's aren't opening or something is binding up. If it ran fine before the engine build, than maybe they put something together wrong on the rebuild. There are cables that run down to those controls, check and make sure they aren't twisted or broken.

 

[Mystic1350]

this started happending subsequent to engine build...i also note that the cables move when i rev it over 3200 rpm as well
i bought seafoam so img onna try that today...maybe they are just stuck
however my problem is that it hesitates under 3200 (2000 rpm range is the worst) in which i didnt think IMRC would effect this as i thought it opened up over 3200

 

[mustang_jr+]

How do your plugs look? Have you replaced the original spark wires?

So strange you're not throwing a code.

 

[Mystic1350]

cleaned the IAC and MAF. Also seafoamed car the 3 ways and still hesitation..Spark plug wires look fine (under 2 years old).
FINALLY THREW CODES and reasearched the hell out of them. this is what i know for each code
P0411-Relates to EVAP--all connections look good, actual valve was replaced 2 years ago

P1132 & P1152- relates to 02's- not sure if my header leak is causing them to be all banged up and misread. i doubt they could have just gone bad.. I Have yet to get under car and check connections. I also have the MIL's for my longtubes

P0300 & 0301 - relates to misfire, i have checked wiring and firing order of wires and everything
normal, wires as i said above are fairly new. could it be bad plugs that jsut went bad?

P1000- relates to drive cycle, wouldnt impact driving

P1270- rev limiter exceeded- from what i read this wouldnt impact driving

ANY Thoughts on the above for my hestitation problem from 2k -3k?

 

[phoenix99]

maybe you can install a new fuel filter?
I had the same problem with my engine and I installed a new fuel filter and it's all gone !

 

[mustang_jr+]

Make sure the o2 sensors are ok and change the fuel filter if it hasn't been done recently.

 

[Mystic1350]

hey guys, just replaced fuel filter and went under car and tightened up 02 sensor that was kinda looose. Problem is still there. is it possible that it needs to be tuned to correct A/F ratio and timing? i got nothing to crazy, but my engine was bored, heads ported and got a full exhaust just recently. HOWEVER it drove great when i first got it but this extreme Hesitation came outta nowhere! it is still real bad between 2k-3k, and sometimes worse at higher rpms, but when it isnt hesitating-it drives perfect. Like i have said above i do have a header leak that is only gettin worse. could be banging up the 02 readings before the cats? I was thinking maybe changin the plugs (which are new from the rebuild, however they could be gapped wroong adn crap brand). i dunnoooo!! its driving me crazy tho
any more thoughts? maybe EGR valve although the codes about that have indicated that.
thanks guysss

 

[Mystic1350]

sooo. knock on wood it appears as if a American Muscle mail order tune has corrected the hesitation problem thus far...i know mail orders arent the best but at least im under the impression that the computer is somewhat corrected.

 

[mustang_jr+]

Sounds odd, you think the computer was getting inaccurate?

 

[Steve491]

Ditto on the IMRCs. A cable could be bend/frayed/ or popped off. The IMRC technology is great but the engineering could have been better back in the 90s.
It may or may not throw a code depending on the situation. For example: If one cable broke or popped off, NO code, just runs like crap over 3200. If they are stuck then a code will register. Like I said, good idea, poor engineering.
Electro-Mechanical is in the past. It's all electric now.

 

[Mystic1350]

The tune thus far knock on wood as seemed to correct the issues...it had to be computer related or relates to mis reading due to header leak