Bad Idle slight hesitation

S

SlickTR

Active Member
Joined
May 29, 2007
OK here is what the car is doing, It will idle rough (low and almost die) it has died on me a couple times backing out of the drive way. just off idle at real light acceleration (foot barely on the pedal) there is a hesitation. Under heavier acceleration and under boost it runs like a top, smooth and no problems at all. occasionally letting off the gas and coasting the idle will kind of lope like it has a big ass cam in it then calm down if I give it a little gas again. The weird part is that it is only when the engine has ran for a while and is hot and in closed loop. when it is cool and hasnt been running for long it is fine, idles great and no hestitation off idle. I know what it's not

-No codes
-No vaccum leaks
-TPS is fine on DS
-not the EGR (has been removed with block off in place, didnt help)
-Not the IAC (i replaced that and set correctly, didnt help)
-Had the ignition module tested and it was fine
-O2 sensor is new and cycles quickly
-Fuel filter is new
-injectors and spark plugs are rather new
-fuel pump is upgraded and hotwired and my fuel pressure's good
-maf is new (full throttle mega maf pipe and g/s is within specs on DS)

-The Coil pack ohmed out fine but I thought since it only does it when it gets hot maybe the coil was bad when it got hot. Well today I replaced it with a Borg Warner unit (it ohmed at 12.5K across all three). The problem seems a little better but is still there, now I'm really confused. I'm thinking since it kind of helped but didnt cure it maybe its still spark related and could be the plug wires (msd 8.5s, age unknown), can these be fine cold and crappy when hot? If it's not the plug wires what else can it be that would cause this only after the car is hot and runs for a while??? you would think that if it was a bad sensor/vacuum leak/ground problem, etc. that it would happen all the time but it doesnt :confused: HELP
 
What is your tps voltage with engine idling?
What is your IAC counts in gear engine running?
 
my car had the same symptoms not too long ago and I found the maf wires had got against the a/c pulley and rubbed one of the maf wires in 2. spliced it back together and good as new.

maybe your problem is this simple.
 
oneslobuick said:
my car had the same symptoms not too long ago and I found the maf wires had got against the a/c pulley and rubbed one of the maf wires in 2. spliced it back together and good as new.

maybe your problem is this simple.
Click to expand...

Would your car only do this when warm and running a while?
 
I had a on again off again love hate with that 4 nch pipe, I installed a screen infront of the sensor to even out the airflow...it helped alot
 
Would your car only do this when warm and running a while?
Click to expand...

it was intermitent. I guess because the wire would make and break but it did run best when making boost like you said.

just a thougt.
 
need more info.

mcasteel2112 said:
I had a on again off again love hate with that 4 nch pipe, I installed a screen infront of the sensor to even out the airflow...it helped alot
Click to expand...

More info.....on the screen---what type of material,placement and ECT.........
THANKS for the info.
 
OK the screen im using is from a impala maf, Now I tried to finaggle a few different ways to cobble it in and in the end i went to advance auto in thier measly performance isle and they have these cheap tuner air filters BUT they come with differet sizes of couplers.

I got the filter kit for about 17 bucks...Kept the couplers, threw the dumb filter away.

the screen fits into one of the couplers which fits into the 4 inch piping, I had to experiment to find where it worked best which came out to just where the Elbow comes through the core support, I had it too close before and it was too much restriction.

I had a 4 inch back in mich but forgot it, so im using the impala screen for right now

Without the screen it was ok with cold air piping untill I slowed down to a red light and it was like the maf was trying to find itself

IM also running a tornado in the 4 inch pipe close to the turbo inlet...got rid of most of the surge i was having

HTH's
 
2 easy checks. The torque converter is unlocking isn't it? Also after the car is running you can unplug the cam sensor and see if it runs better to see if that is the problem. I had a light accelaration miss that was the cam sensor.
 
XLR8 said:
2 easy checks. The torque converter is unlocking isn't it? Also after the car is running you can unplug the cam sensor and see if it runs better to see if that is the problem. I had a light accelaration miss that was the cam sensor.
Click to expand...

TC is fine, I'm leaning towards Cam sensor at this time. I wont be able to check the car for a few days but I will report back and keep you guys updated, THANKS!

btw, all the wires connectors and grounds looked good from a visual check.
 
Did you clean your idle air sensor and throttle body?
I also noticed with my GN is that in the summer months I need a little less fuel pressure than the winter months. If i don't back off a couple pounds of pressure in the summer mines runs just like your saying.
 
trx#9 said:
Did you clean your idle air sensor and throttle body?
I also noticed with my GN is that in the summer months I need a little less fuel pressure than the winter months. If i don't back off a couple pounds of pressure in the summer mines runs just like your saying.
Click to expand...


Yep like I said in my first post the IAC is brand new and I did clean out the housing and TB before replaced the IAC all together. I've played with the tune alot to no avail, I guess just backing off the fuel pressure a couple pounds it worth a shot, I will try that too.
 
Did you check the IAC from pintle tip to the base? needs to be under 1 1/8

the after market ones from advance/autozone dont come turn key, you have to messure then adjust by pulling spring back and turning pintle in
 
mcasteel2112 said:
Did you check the IAC from pintle tip to the base? needs to be under 1 1/8

the after market ones from advance/autozone dont come turn key, you have to messure then adjust by pulling spring back and turning pintle in
Click to expand...

It was AC delco from kirbans. When I get back to it I'm going to eliminate these possible causes

1. Even though I found no leaks last time I'm going to replace all my VAC lines and replace the PCV with a genuine AC Delco piece (not a bad thing to do anyway)
2. Unplug cam sensor and see what happens.
3. Play with fuel pressure if 1 and 2 dont solve it
4. Plug wires (I'll swap out for a brand new set and see what happens)
5. If 1 2 3 and 4 fail then I need to find someone close that has a different maf and intake I can swap to see if it is the mega maf pipe
6. If none of this works then I'll swap on a new crank sensor

I'll keep everyone updated, Thanks again for the help guys!
 
OK guys, sorry for the delay, Uncle Sam has been keeping me REAL busy lately...anyway got back to it a little today

1. Replaced all the vac lines, replaced PCV with correct AC Delco and the PCV grommet (holy cow that grommet was a job!). Idle improved but still seems just a bit low but it hasnt loped letting off the gas while driving anymore which is good. How ever it still had the tip in stumble so I moved to the next thing

2. Unplugged the cam sensor and the car stumbled a second and died, is this what is supposed to happen? I thought is was suppose to keep running. Advice please, I stopped there for now
 
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