High idle

[mikewats]

Hello, I bout my ranger a couple years ago and well, it was a turd. I drove it till it died and rebuilt it from the ground up. It's a 94 XLT with the 4.0 OHV, single cab long bed, 5 speed, had ac but I took it out and added an ac bypass pulley. The maf assembly was chunky and had to go bc of the plans I had for the truck, so I converted it to use modern slot style maf sensor and it works great. I've been working out kinks little by little the past few months now that I have it back on the road, buy I can't seem to solve this high idle issue. The truck would idle at about 1.3x to 1.5k rpms, so I set the throttle screw as low as possible and it now sits at about 900-1000. Throttle body is good, tps is good, maf is good, no vacuum leaks, this truck has no pcv or egr, if I unplug the iac the rpm does not change like it normally would. I've gone over this thing with a fine toothed comb and can confirm there are no vacuum leaks. The obd1 port under the hood doesn't seem to do anything, and I know my scanner works bc I used it on my 94 explorer, so I'm really relying on what I know as a mechanic. When I first start the truck when it's warm, it will sort of surge for about 10 seconds but will idle where it's supposed to. After that 10 seconds, it shoots back up to 900-1k rpm. The only thing I didn't replace on this engine is the iac, but it's pretty clean and the valve moves freely. Any help would be appreciated it's got me stumped

 

[bobbywalter]

what is the idle vacuum?

 

[bobbywalter]

are you sure the brake booster is not leaking? no pvc? as in a catch can? did you plug the port on the air tube?

plug that and the brake booster. unplug the maf... and plug the iac off. what happens then?

 

[mikewats]

Honestly haven't checked! I will check tomorrow when I'm at the shop. Do you know what it is supposed to be?

 

[mikewats]

are you sure the brake booster is not leaking? no pvc? as in a catch can? did you plug the port on the air tube?

plug that and the brake booster. unplug the maf... and plug the iac off. what happens then?

Not sure what you mean by "air tube" do you mean the valve cover vent? And yes my truck came from factory with no egr or PCV, I believe only the California trucks had it. I unplugged the iac tps and maf, and it still held at high idle. I took the iac off last night and plugged it off and fell on it's face when I tried to start it, adjusted the throttle screw enough for it to run and it still did it! I will have to try plugging off the brake booster line and see if anything changes

 

[bobbywalter]

so there is just a rubber plug on the shelf in the rear drivers side valve cover? i am looking right at it in the pic.

and the oil fill tube vent that is supposed to be feeding the intake tube is just open to atmosphere?

all of the evap tubes hooked up or capped? stuck open purge valve will give you higher idle.


the other potential issue is the custom intake itself.

 

[bobbywalter]

as to idle vacuum. assuming stock camshaft and valvetrain/compression. 17 plus.

what is tps voltage at idle?

 

[mikewats]

as for the valve cover vent on the passenger side valve cover it is not open I have a small filter on it until I can get a catch can for it, I will throw a hose from the passenger side to the intake somewhere between the maf and throttle body, I didn't even think about that honestly. And I tested the purge valve and it functions how it should so I'm not really too worried about that. Hopefully the pcv will help this, I will probably also replace my iac because it does jump around a little bit while idling sometimes but I'll try the pcv tube first

 

[mikewats]

so there is just a rubber plug on the shelf in the rear drivers side valve cover? i am looking right at it in the pic.

and the oil fill tube vent that is supposed to be feeding the intake tube is just open to atmosphere?

all of the evap tubes hooked up or capped? stuck open purge valve will give you higher idle.


the other potential issue is the custom intake itself.

Oh no my bad the pcv is hooked up on driver side but I just took the valve out and heard a rattle so I shook it and the little plunger inside the valve is just loosey goosey, so I plugged it to see if it would change idle and it didn't. Still going to replace it seeing as it isn't functioning properly tho. I just picked up a new iac, I'll probably install it in the morning and see if it changes anything

 

[bobbywalter]

Oh no my bad the pcv is hooked up on driver side but I just took the valve out and heard a rattle so I shook it and the little plunger inside the valve is just loosey goosey, so I plugged it to see if it would change idle and it didn't. Still going to replace it seeing as it isn't functioning properly tho. I just picked up a new iac, I'll probably install it in the morning and see if it changes anything

so you have a steady 17 plus on a vacuum gauge?


if you buy anything. buy a vacuum gauge.

 

[bobbywalter]

Amazon.com

Amazon.com

 

[mikewats]

I'll throw one on it in the morning before I replace the iac, didn't get a chance today. Gonna see if I can find anywhere that has a new pcv valve too bc that thing is toast. Will update tomorrow

 

[bobbywalter]

I'll throw one on it in the morning before I replace the iac, didn't get a chance today. Gonna see if I can find anywhere that has a new pcv valve too bc that thing is toast. Will update tomorrow

it is supposed to click if you rattle it. it is generally a check valve. but....if it is not sealing in the seated position it is failed. though...some systems it is just a pinhole and a controlled vacuum leak configured into the operating system.

there are several ports at the throttle body and the one that goes to the evap valve can leak and be nearly undetectable.


from there a leaking injector could be high idle but usually a miss is obvious and a surge along with o2 codes.

 

[mikewats]

Yeah it's rattling like a marble in a soup can lol, a lot more than it should, seems like the spring is totally wore out. I Will definitely look into the throttle body port, I didn't hear any vacuum leaks and I hit all the vacuum components with some ether, nothing. So I will have to look into that a little bit for sure. As for the injectors, they are brand new and I tested each one before installing and it runs smooth, so tbh I think I'm safe. I just looked at my throttle body, and it only has 1 port. The line on that port is goin to the fpr. Kinda odd no? This truck was in complete shambles when I bought it, I've had to re wire just about everything, and troubleshoot a lottt of shit lol. It's has no evap canister, just a purge valve with an open line on what would have been the canister end. Purge valve works, I just tested it. Is there supposed to be a line that goes from the canister to the throttle?

 

[bobbywalter]

i am also assuming you are in new jersey and near sea level or at least under 1000 feet.


you lose around 1 inch per 1000 feet above sea level. just putting this here in case