Topic: Bounty Hunter / Your Advice on Rough Idol

[jonzjeepyj]

After doing the 4.0L TB upgrade , I have been throwing a code on the Jeep that is a  #13
*Manifold Absolute Pressure (MAP) Sensor Vacuum* code.  Could this be due to the TB upgrade?
I'm not running a wide band O2 sensor which ties in to all this.  I did use the TB of a 96 and newer
Jeep and capped off the extra port for the map sensor.  Or is it the MAP sensor going bad.

When I start up the Jeep in the morning to warm up, after running for about 20 seconds, the idol
drops off and it runs really rough for 3-5 seconds and then returns to a normal idol.  This will throw the
check engine light.   If I stop and start it up again , the check engine light goes off and I notice nothing
wrong.   

Your opinion on what it might be?

O2 Sensor ?
MAP Sensor ?
The Jeep adjusting to the larger TB ?

Thanks,  John

[Mr_Random]

Did you change the IAC motor and housing?

[jonzjeepyj]

Yes,  I reused the 2.5L IAS on the 4.0L TB

[jonzjeepyj]

This started 2 weeks after I installed the 4.0L TB.  It ran fine for 2 weeks and only started
doing this a few days ago.  It runs and drives fine after it returns to normal  with no other
symptoms except for the thrown code. 

The check engine light goes off and no more problems or symptoms.  If I get in it and drive
imeadetly,  it does not happen?

[jonzjeepyj]

Just thinking out loud,

Could it be that I'm NOT running the wide band o2 sensor and it cant adjust fast enough in the cold weather?
Could it be an intermittent problem and the MAP sensor is going bad?
Due to me upgrading the TB and boring out the intake, is it just adjusting to the larger air flow?
Or is a a vacuum problem and it's not sensing the air flow at the TB / Bad venture?

Again,  I'm just throwing out some ideas
John

[Mr_Random]

Dang... you've got me stumped...

I'll throw this one out there too; did you restart the system by touching the positive battery cable to the negative terminal? Should drain any capacitance in the ECU...

I know it was a dumb question, but may have missed it?

And I doubt you should need a wide band O2... it's not THAT much more air flow (nothing like forced induction at least)!

And you didn't say whether you re used the 2.5L IAC HOUSING too... I'm pretty sure they are different... I'm not trying to insult you or anything, just being thorough!

[Bounty Hunter]

Your problem is not common to the 4.0 tb or 62mm tb upgrades, nor is it related to the o2 sensor.  Your stock sensor is fine, wideband is primarily used for an AFR guage.

Make sure you used the 2.5 IAC & IAC housing, and the IAC gasket is intact and housing is tight. 

I recommend a good bench cleaning of the TB & IAC.  Then try a different MAP sensor.

As a last resort, buy one of my 62mm TB's ;-)

[jonzjeepyj]

Just to restate,

I did use the 2.5 IAS motor and housing and all sensors
off the 2.5 TB on the 4.0L TB  I bought a new gasket
from NAPA and replaced the old one.  I did not ground
out the ECU for 30 secs. yet but that would only clear
the codes, Not solve the problem.

I think a good bench cleaning is in order also.  I also wanted
to try Sea Foam through the motor.  It doesn't happen every time
I start it up either.  I'll do the cleaning and Sea Foam and see
what happens.

Thanks, 
John

[chardrc]

I remember someone had a problem where the bushing for the shaft that the throttle plate(probably wrong word but...) is connected to went bad and let air leak in... but that would happen all the time so

[Mr_Random]

Just to restate,

I did use the 2.5 IAS motor and housing and all sensors
off the 2.5 TB on the 4.0L TB  I bought a new gasket
from NAPA and replaced the old one.  I did not ground
out the ECU for 30 secs. yet but that would only clear
the codes, Not solve the problem.

I think a good bench cleaning is in order also.  I also wanted
to try Sea Foam through the motor.  It doesn't happen every time
I start it up either.  I'll do the cleaning and Sea Foam and see
what happens.

Thanks, 
John

Grounding the ECU would not only clear the codes, but reset the a/f maps that the ECU has learned from your old system. I think it takes 40 warm-up cycles for the computer to "learn" your engine's correct maps.

[Bounty Hunter]

Correct, but it's 50 warm-up cycles.  Probably a good idea to speed up the HP and mileage gains.

Yes occasionally the throttle shaft bearings/seals will wear out and cause a vacuum leak, generally leading to a high idle.  But I think it would happen more regular that what he's describing.

[tallrugbyguy]

i would reset the ecu. after i did my swap i had a messed up idle at times. then i got a new ecu shartley after due to the old one dyeing and all problems fixed.!

[jonzjeepyj]

OK,  I'll ground and discharge the ECU to wipe everything off and go from there.
It was a idling problem but a very low idol and sputter for about 3-5 seconds and
then back to normal.  It hasn't done it again so I will leave it for now.  I will discharge
and ground the ECU right now though. 

John

[Bounty Hunter]

I just read a site that recommended this for resetting the ECU.

Disconnect battery and touch pos. and neg. cables together for 30 sec.
Reconnect.
Turn ignition to run (not start).
Turn headlights on, then off.
Turn ignition off.


I'm not real sure what the headlight sequence has to do with it, but it's not the first time I've seen it recommended.  Anybody else know?

[FourbangerYJ]

Does just disconnecting the pos. on the battery reset anything?