[91GRNGT]

Hey there, i have a 91 gt, and i have been reading on this thing and I can't figure anything out, the problem is this.. Sometimes, maybe 1 time a week or 1 time every two weeks, it will bog a little and bump bump and then backfire a little, can anyone help please? Could this be my IAC or whatever dirty? I unplugged the IAC without any changes to the idle is this normal?? Please help.. If it were timing it would do it all the time wouldn't it??? The car runs very strong till this happens, but once I wait a min and then punch it she runs like hell. Please help...

[ChrisJ]

I would think if you unhooked the IAC it would not run well...

SO if you unplug it and it runs the same I would think it would be the IAC...But I am not 100% positive on it beign the IAC though...

[91GRNGT]

anymore????? Opinions??? Thanks chris...

[stang fanatic]

you probaly wont see much of an idle change when you unplugged the iac unless you were loading up the engine and making it work. all the iac does is control your idle to maintain its set rpm when the engine is loaded up, like turning on the a/c, etc.
sound more like a mass air sensor issue

[91GRNGT]

wonder if i can clean the MASS AIR??? Think contact cleaner will help??

[Screemin3o2]

well the IAC doesn't only control your idle when the car is under some sort of accessory load, it also allows airflow into your engine when the throttle plates are closed. you should see enough of a difference when you IAC is disconnected even when you are idling without a load.

[91GRNGT]

i don 't see or hear any changes while the car is running..

[Screemin3o2]

I would definately try to clean the IAC and maybe replace the gasket. Carb cleaner will do it

[91GRNGT]

ok i did check the iac, and it did go down in idle, and i pulled the mass sensor too, and it idled real shitty but never died then i plugged it back up and it started idling good again... I painted the engine up a little, I have to pressure wash it, and i figure when the paint gets cured up i would go from the top and clean all the old oil off and see what eles i got..

[cali 5.0]

if u unplug the iac while the car is on then the car would cut off....
unless of course u were keeping it on.. i dont understand why u would suspect the iac being bad if the car backfires.. they have nothing to do with each other.. backfireing is usually the case of timing...

[Screemin3o2]

the backfiring shouldn't have anything to do with it but the bogging situation most definately could.

[91GRNGT]

Umm cali, I have no ideal I am picking at straws here, that is why i posted this, don't u think if i knew what the problem was I wouldn't have posted?

[cali 5.0]

no shit but it if it "backfires" every other week then i'd say tht thats not a problem at all so why even include tht..
about the bogging down if u have a friend with a 5.0 then jus swap iac motors and see if tht solves the problem and if it does thn u no tht u need a new iac...

[91GRNGT]

any other opinions ????? Thanks for your input cali, I am intrested in other opinions still...

[stang fanatic]

backfiring is a result of an unburned/or late fuel burn condition in which factors other than timing are involved...its at which time the backfire occurs that leads to which condition is existing

[91GRNGT]

so where do u think i should check?? if it were doing it all the time i would think timing, this i don't think is the problem..

[1slo5.0]

Ignition timing, vacuum leaks, rocker arms too tight (if they are adjustable), bad head gasket.....that's what comes to mind so far.

[stang fanatic]

is when idling, cruising, or throttling (definitely not during coast im sure)?

[91GRNGT]

this only happens like when i go to drive normal sometimes after i drive it a bit sometimes not, this doesn't happen all the time., my egr valve doesn't have a vaccum line to it, also the engine was just built 2500 miles ago, that doesn't mean the headgasket isn't bad just letting ya know.. This happens like if i go out on the street and drive normal it happens, and when i get on it after letting off the gas she will run like hell, this only happens maybe once a week or two weeks, i have had the car for 1 month and it has only happend 2 times..

[stang fanatic]

Man, diagnosis like that are difficult since theres no frequency. clearly sounds like a sensor intermittently acting up, you may just have to wait for a failure to know which one.