Idle issue after IM gaskets

PsYcHo_FrEkE · Apr 15, 2014

1997 Ford Ranger 4.0L EFI.

I just finished replacing VC, IM, TB, Fuel Rail... etc. About all of the gaskets in the upper end to fix a P0171 & P0174. I had to replace the pintle caps on the injectors. I used the generic blue ones from the parts store since they were all that I could find. Put it all back together (all torqued to spec, then upper intake manifold torque re-checked), flushed the engine and the radiator, and it was running great... until it warmed up. I replaced the IAC about 4 or 5 months ago. Warmed up I now have an idle issue that wasn't there before (at least not since I replaced the IAC). IAC checked 10.6 ohms. Seems to run okay going down the road, but tries to (and occasionally does) die when I stop the truck. . I can feel the loss of power as I let off of the accelerator. I'm doubting the problem is fuel related since acceleration seems to be fine. The erratic idle is prominent throughout the full RPM range when sitting in neutral. Currently, there is no CEL. I have posted a youtube video of the problem. In the video I circle the engine to try to isolate the problem if it's a vacuum leak and to double check all of my connections (again).

On a side note when it first started doing it I sprayed some brake cleaner on the upper intake around the seam and the idle straightened out. It only worked one time. I was unable to replicate this. Spraying brake cleaner there now does nothing to change the idle. The only thing I can think of is that perhaps the upper intake manifold is coming apart at the seam or is cracked somewhere underneath. Does anyone else have any opinions on what could be going on here?

http://www.youtube.com/watch?v=1aAfWg3uVKg

RonD · Apr 15, 2014

On warmed up engine unplug the IAC valve and see if idle drops to 500-600rpm and stabilizes.
If so then computer is opening and closing IAC valve for some reason, or IAC Valve step motor is acting up.
If idle is higher and/or still wandering then you have a vacuum leak.

Also check the air plenum from MAF to intake(big air tube), that is a "vacuum" chamber since any air leaking in here is not passing through the MAF so would be unmetered air and cause the same symptoms as an intake vacuum leak.
They often crack on the under side near MAF or intake ends and check rubber seals at both ends.

PsYcHo_FrEkE · Apr 15, 2014

Inlet tube is good... everything plugged into it as it should be, nothing loose, no cracks, etc. Warmed up the truck and unplugged the IAC. The engine stalled out.

RonD · Apr 15, 2014

PsYcHo_FrEkE said:
Inlet tube is good... everything plugged into it as it should be, nothing loose, no cracks, etc. Warmed up the truck and unplugged the IAC. The engine stalled out.

Stall is good, but would be better to set it up right at this time.
There should be a screw on the lower throttle linkage, this is in essence a no stall adjustment in case IAC valve fails, not an idle screw although it can control idle.
On warm engine, use this screw to open throttle plate a little more then restart engine with IAC unplugged.
Repeat until engine idle is 500-600rpms, should be steady idle

Then hook IAC back up and see if it settles down at 700-750rpms

I would unhook negative battery for 5 minutes(reboots computer) after adjusting the screw as this will change TPS(throttle position sensor) voltage and computer will need to relearn it

PsYcHo_FrEkE · Apr 16, 2014

RonD said:
Stall is good, but would be better to set it up right at this time.
There should be a screw on the lower throttle linkage, this is in essence a no stall adjustment in case IAC valve fails, not an idle screw although it can control idle.
On warm engine, use this screw to open throttle plate a little more then restart engine with IAC unplugged.
Repeat until engine idle is 500-600rpms, should be steady idle

Then hook IAC back up and see if it settles down at 700-750rpms

I would unhook negative battery for 5 minutes(reboots computer) after adjusting the screw as this will change TPS(throttle position sensor) voltage and computer will need to relearn it

That didn't do it...

RonD · Apr 16, 2014

Didn't do what?

It wasn't meant to fix anything, it was to get a low idle so you could find out if the IAC valve or a vacuum leak was causing the wandering idle

PsYcHo_FrEkE · Apr 16, 2014

RonD said:
Didn't do what?

It wasn't meant to fix anything, it was to get a low idle so you could find out if the IAC valve or a vacuum leak was causing the wandering idle

My mistake. Thankfully your fix did get me through the night, though. I wasn't sure how I was going to work with the engine dying. Just for grins I replaced the IAC (took it back, too). I had already checked the IAC with a meter, but I wanted to be certain that it wasn't something mechanical. The IAC is not the problem. I keep leaning towards a vacuum leak but I can't seem to detect it. Not even with starter fluid.

I have also checked the TPS. After running about 80+ miles last night there is still no CEL.

PsYcHo_FrEkE · Apr 17, 2014

I still haven't found the vac leak, but I'm starting to get this sinking feeling that I may have to take the lower intake gasket off and replace it (again). Three reasons:

First, when I was putting it on I accidently over-torqued a couple of bolts and then backed them off because my clicker wasn't working right.

Second, I used the Victor Reinz 2 piece gasket instead of the Ford 1 piece.

Third, because I know it's possible with using a two piece gasket that I may have disturbed the bead of silicone on the area where the lower intake meets the block. With a one piece gasket I wouldn't have needed a bead all the way across.

I really don't look forward to ripping all of that apart again if I don't have to... :sad:

I should be able to re-use the valve cover gaskets I just replaced, right? Just wondering if I'll be able to get all of the RTV off of the rubber parts of the gaskets (near the upper corners).

PsYcHo_FrEkE · Apr 17, 2014

opinions?

RonD · Apr 17, 2014

If you doubt the intake gasket then redo it.

PsYcHo_FrEkE · Apr 21, 2014

Anyone know what this is or where it goes? Fell out under the truck... Don't remember taking anything off that looked like this.

RonD · Apr 21, 2014

Doesn't look familiar?

Almost rad hose size?

PsYcHo_FrEkE · Apr 22, 2014

False alarm.. just the boot for the plug that goes to the coil pack.

I've replaced the IM, Valve Cover Gaskets, and fuel manifold gasket (again). Truck is still doing the same thing. I did hear a rattling that is new, though. Sounded like it was coming from the EGR valve, but I'm having trouble pinpointing it exactly. Still no CEL.

I usually don't throw parts at a vehicle like this. Usually I've got everything researched and have the part narrowed down. This is making me crazy *smh*...

PsYcHo_FrEkE · Apr 23, 2014

Fuel pressure is running at 32psi (42psi with regulator disconnected). Is this right?

RonD · Apr 23, 2014

Spec is 40-50psi
Also if possible check fuel pressure gauge on another engine or even a tire that has a known pressure, gauges can read a few pounds off so best to have a baseline test of a known pressure.

Fuel pressure regulator(FPR) is opened and closed by vacuum pressure in the intake.
Vacuum is highest at idle so fuel pressure would be lowest at idle.
Pull off the vacuum line on FPR and check it for fuel smell, if fuel is present replace FPR.

42psi is a bit low with FPR's vacuum line disconnected, this would either be from an older fuel pump or a small leak.
What was fuel pressure with engine off, it should drop a few pounds then stabilize, and stay without dropping any more, if it continues dropping then there is a leak, if there is no gas smell anywhere then could be FPR valve or an in tank leak, i.e. fuel pump check valve(back flow preventer)

But the 32-42psi should be fine for engine operation, the computer would open injectors longer when O2 sensors report leaner burn from lower pressure.

Idle issue after IM gaskets

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