86 2.9 dtc 18 rough idle and stalling

[daduke]

I recently bought an 86 ranger 2.9 manual not running off craigslist. i replaced the fuel pump in the tank and the fuel pump wiring connectors and now it runs. my current Problems are that if I sit and let it idle it will run for a little while and then just get slower and slower till it finally just dies . If I'm driving it, it will usually stall at stop lights until warm. and will periodically start to chug and try to stall but if I let off the gas and leave it in gear it will get over it or if I floor it it will sometimes fix itself too. ive ran computer diagnostics on the koeo test i get a code 18 for missing tach signal and a code for the egr which has been removed. koer test wouldn't complete but the scan tool i used is known for being flaky.

on a separate note I was going to check the base timing because I have a strong inkling someone has futzed with the distributor. ( the tfi plug cant be removed because its pointing into the valve cover) but I can't find the hold down bolt for the distributor and I don't want to check something I cant fix.

 

[RonD]

The Computer(PCM) controls the idle on fuel injected engines, there are no jets so an idle screw won't work.
It does this by opening and closing the IAC valve located on the upper intake, by the throttle plate.
The missing tach signal code could be the issue here, not sure if this refers to the PIP or tach??, but the computer needs to know the engine RPMs to set the idle.

On normal startup with cold engine the computer will set idle at about 1,100rpm
As engine warms up idle will slowly drop to 800rpm(automatic) or 700rpm(manual)
If this isn't happening then either computer doesn't know what RPM the engine is at or the IAC Valve isn't working.
With engine warmed up and idling unplug the IAC valve wires, RPMs should drop to 500rpm or engine may stall, if idle doesn't change then computer can't control IAC valve so it may be bad.

The screw on the throttle linkage is NOT an idle adjustment, it is for adjusting TPS(throttle position sensor).
If you have played with this try to reset it, with engine warm and IAC Valve unplugged set screw so idle is at around 500rpm, then plug IAC back in.

Good read here on the TFI system: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

 

[adsm08]

Well, to be fair the screw on the throttle is also used for idle adjustment.

Proper procedure is to bring the engine to temp, hold the engine at 2000 PRM for 2 minutes, place the calibrated orifice (about 3/32" across) in the PCV line, unplug the IAC, and then turn the screw until you get the idle speed you want.

But don't do that, it isn't our problem.

 

[daduke]

thanks for the link on the tfi system. i understand there's no idle adjust screw my iac valve was very recently replaced. and it seems good. heres a video of my truck idling http://youtu.be/s3us3nXhQ_s

 

[daduke]

i found the hold down bolt got the base timing set it was a little retarded. put new plugs since the old ones were very black and ugly, its running alot better but still complaining. completely checked the ignition system its fine, fuel pressure is fine. our only thought now is that maybe the fuel injectors are partially gunked up from it not having a fuel filter when i got it.