i've 1,500 miles on an overhauled EFI 302 1986 F-150. i've put in: throttle position sensor, egr sensor, fuel pressure regulator, high pressure fuel pump.
still there is a fluctuating idle and a hesitation when accelerating from idle. i'm lost with this and at the bottom of my wallet. could this be electrical? any help would be great.

 

Clean the throttle valve area with carb cleaner. Also the IAC control solenoid mounted on the throttle body.

 

do you mean throttle air bypass valve? IAC control solenoid? i have a chiltons manual and i can't seem to find it.

 

Q#1: is the surge random or timed to the engine
Q#2: How much did the rebuild cost.

Depending on the answers above, it may be a problem with the engine itself. Plus, I'd check for a vacuum leak at the base of the intake. If the heads or block were planed, it screws up the angle with the intake. Also, did you put any sealer on the intake gaskets? You should have........

Jared

 

[updated:LAST EDITED ON 05-Nov-02 AT 00:39 AM (EST)]the fluctuation is random. usually it will pull down rpms, then up, etc. almost like it is looking for a place to set. it's about a 200 - 300 rpm fluctuation around 800 rpms.

cost: $1,750. i know the guy that did it and i trust he did the job right. he told me that there were still problems with the computer part of it (he did not have the equipment to test it). i had it tested and put in the parts i listed earlier.

with everything so far: $2,300. i did not expect this price and headache. my original plan was to put in a 351W, but people i talked to suggested against it. with the money i've spent i think i could have easily gone with a 351W.

 

88grandmarquis, I'd go with franklin on this one. Does not cost much but a spray can of throttle body cleaner to do this. This cleaning mentioned here has solved this same problem many times on my 94 Aerostar and other EFI Fords I've had.

 

alright, i sprayed throttle body cleaner in it. turned out that it was pretty dirty. i sprayed a little into the holes that go to the IAC control (i think that was it). the idle went from 800 rpms before cleaning to 1200 rpms after cleaning (no adjustment made).

the throttle control rod had a tiny, tiny bit of looseness in it. you can't even see it when you turn the engine throttle lever, BUT when you do turn the idle down (that tiny, tiny bit) it will start to fluctuate (less than before, though). turn it up, it's fine.

the hesitation: when you hit the accelerator and it hesitates, there is a air sucking sound at the throttle body. is this normal? could it be due to something else?

i've scheduled another appointment with yet another mechanic for next week. it will be another $50 for the comp. diagnostics and extra cash for the rest of the checkup. i hate to be spending all this money.

ALSO ---> the point on the ignition coil looked corroded/in bad shape when i put in new plug wires. could this have an effect?

 

Onething to check is the mass air flow needle inside... if it gets gummed up it wont let the truck idle down... thats the first thing that comes to mind
Godbless Quads

 

quads
'86 didn't have MAF - that was '95 (CA 5.0L) & '96 (all 5.0L & 5.8L).

86GM
The IAC is mounted to the throttle body & looks like a motor sticking into an aluminum casting with 2 screws holding on the TB. The connector only has 2 or 3 wires.

You can pull the codes yourself for free anytime you want. http://www.broncodata.com/tech/codes.htm Haynes manuals have it, too, but my code list is more complete.

 

damnit, now it's idling fast. i've adjusted the throttle screw just to control it some. i can unplug sensors and there is no reaction. looks like it's back to the garage on monday.


i'll let you know what they say, see if they are pulling my legs out from underneath me.

 

i noticed one thing when i was poking around on the motor: it was filthy/grimy in the throttle body and intake manifold. i thought that when you overhauled an engine that you also cleaned the used parts. because of this i have lost some faith in the guy that did the work.

 

Did you get the motor fixed?


'89 302 AOD Bronco, Grant wheel, 31" tires, JVC remote CD,

 

yeah, i cleaned the IAC valve and it runs good. i'm still going to have to clean the upper intake manifold, but i will wait till spring for that.