zacharoni16

I have a 1991 Ford Ranger with EFI 4.0 V-6. It idles really rough on cold starts, and it seems to idle even worse if the outside temp is cold. Also, when you put it in gear (automatic) it sometimes stalls out. If it stalls, I can't restart it without pumping the gas while turning the key. It idles a lot better and doesn't stall when it's warmed up fully, but it does sometimes hesitate.

I already changed all the plugs, plug wires, PCV valve, fuel filter, IAC valve, TPS sensor, checked the Air charge sensor, checked the ECT sensor, and I cleaned the MAF sensor. Nothing seemed to help.

Anybody got any ideas?

I pulled the codes and the only one I'm getting is the HEGO is not switching, but I don't think that would cause all my symptoms and it's usually not the oxygen sensor anyway that throws that code

RangerPilot

I have a 1999 4.0 V6 Manual that has the same symtoms (no stalling). On cold morning starts (practically all winter...the colder the more obvious the problem)...the truck will start to idle around 800 RPM. The roughness will begin to slightly shake the truck...it almost sounds like a plug is missing however after some time the idler kicks in and revs it up to 1200 RPM or so and the process starts over again.

When driving there are little problems and I am not stalling out. Lastly, on cold mornings...after starting to drive and coming to a routine traffic stop the truck will idle higher than normal until a complete stop and then it takes a while to return to a normal idle...this is not as noticable on a warm morning.

I have a fairly new IAC valve.
156,000 miles

Thanks in advance

zacharoni16

I'm beginning to think this is a fuel pressure regulator problem, but I don't have access to a fuel pressure gauge. The colder it gets the hard it is to start, and I have to keep pumping the gas to keep it running until it warms up.

It may be the cold start valve?

BLACKSNAKE427

I Had The Same Problem And Everyone In Montana Was Telling Me It Was The Fuel Pump-- I Did Not Agree I Spent About 70 Dollars On A Fuel Pressure Regulator And It Started Up Better Than Ever And Power I Did Not Know I Had. Replace The Fuel Pressure Regulator And Ten Minutes Putting It In. If You Want To Test It Just Take The Vacuum Line And Suck On It Then Put Your Tongue On The End If The Vacuum Line Holds Indefinitly Its Good But If It Takes Awhile Your Diaphram Is Shot Which Means Your Pressure Is Not Holding.

RangerPilot

Well...I gave up the goose and took it to Ford. I will post the results of their findings tomorrow once I get it back.

I think it is either the vacuum leak or like previously mentioned a fuel pressure problem...the Check Engine light reads that I am "running lean" however I notice no problem with MPG so I am not quite sure.

RangerPilot

The Result is in...

The problem with my truck in regards to the idle problem is

Intake Gasket(s) Leak

Again, I was not having a problem stalling so it could be different for other vehicles but have someone pull the codes to see if they can isolate a leak.

My codes were 171, 174 and 1131...all a result of a leak.

Ford is quoting around $550 to repair, mostly labor since a gasket won't cost too much. I will get the truck back Monday (hopefully) so I will post back with the total cost and work performed.

Good Luck...Everyone else.

havokprime

Got kinda raped for that price man. Gaskets are not that hard to put in, let alone not that expensive to buy.

RangerPilot

Yea well, I would have asked for volutneers to do it for free but I didn't think that would get much response.

I usually do all the work myself but this one was beyond my level since I didn't even know how to find the vacuum leak. Ford had to blow smoke through it in order to find the problem.

I was fully aware of that Ford would cost an arm and a leg but you gotta do whatcha gotta do. I'd rather spend the 500+ and know it is done with a guarantee then to break down somewhere and waste $80 + on a tow truck.

I don't have loyalties to any personal mechanics so its the price I am willing to pay to have it done.