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Poor Idle????

Joes4x4Ranger

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The center of Hell, Parker, Arizona!
Year, Model & Trim Level
'91 XLT
Alright, how smooth is a stock 91 4.0 W/Manual Trans supposed to Idle? I just put in a Motorcraft Reman engine, and it idles shitty, just like the blown head gasket POS I took out. No CEL, No Codes, just a shitty idle. When I swapped parts over, they were METICUISLY CLEANED. Every part of the intake system was cleaned better than a 5 start restaurant plate inside and out including the MAF. Fuel injectors replaced with NEW Design III. New plugs, and wires, new air filter, IAC and O2 sensor replaced last year.

Why won’t this thing Idle smooth and steady? It has a rough, rolling Idle, inside the rig I see the TACH fluctuate 50-75 rpm and the gear shifter shakes. With the hood open I can see the engine shaking slightly like a vacuum leak. EVERYTHING IS TIGHT. All plastic lines were scraped and new rubber lines installed. I unplug the MAF and the Idle is 200 RPM higher and steady, but the engine still shakes. I unplug the IAC and it nearly stalls. Could the PCM be puked? The one area I have not gone after is fuel filter( looks very new) and Pressure regulator. I’m in the poor house because of this POS truck.

I'm expecting a ROCK SOLID SMOOTH AS SILK IDLE. I want to be able to balance an egg on the hood with the engine running. I want it to idle so smooth I can’t tell its running. AM I ASKING TOO MUCH???? IS THIS POSSABLE FOR THIS ENGINE???I just spent $2200 for the long block and the Mother F###er still runs like shit. FRUSTRATED FRUSTRATED, FRUSTRATED!!!! If the blue book valued the piece of shit higher than the long block cost I’d full insure it and drive it into Lake Havasu.
 
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Tbars4

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..Just throwing some things out there...

...At first I was going to say your MAF...Second, I was wondering if you replaced your vacuum lines, but it looks like you covered that..:scratch:

...What procedure did you use to time the motor??? And maybe you have a sticky solenoid purge valve???
 
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Joes4x4Ranger

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...What procedure did you use to time the motor??? And maybe you have a sticky solenoid purge valve???

It is a 1991 I could not find a timing procedure. No Cam Position Sensor, the only reference for spark and fuel would be the Crank position Sensor. If there is a timing procedure for this engine tell me. I'll do it.

How do I check the purge valve?
 
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Explodr94

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This is just an opinion, but the first thing that came to my mind was ignition pack. I have had a rough idle several times. Once is was a fan blade had come off the fan. But when these ignition packs go bad the car runs like crap. Just my two cents.
 
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Tbars4

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...^^^ That is definately something I would check first...:thumbsup:...Coil packs do go bad frequently...

...Dumb question but, did you pull the little timing plug to time your motor??
 
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Joes4x4Ranger

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...Dumb question but, did you pull the little timing plug to time your motor??

I did nothing to adjust, change or alter timing. I have no idea how to change the timing on this engine. I was under the impression that without a cam sensor the timing could not be changed/adjusted. PLEASE TELL ME HOW TO ADJUST THE TIMING. I have a 1991 withNO, I repeat NO camshaft sensor
 
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MrShorty

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There's no way to adjust ignition timing, but you can check it. Pull the SPOUT connector (on my '92, it's in the bunch of wires coming out of the coil pack). Locate the marks on the crankshaft pulley and highlight. Hook up timing light to #1 and point at crank with engine idling. Timing should 10 BTDC. If it's not, double check the balancer that it hasn't rotated (in other words, the TDC on the crankshaft pulley corresponds to TDC). If the base timing is wrong, then we'll have to figure out how to diagnose that, but it indicates that something is broken somewhere.

Speaking of timing, you are certain that the spark plug wires are routed correctly?

The other timing to worry about is the valve timing. Presumably, the remanufacturer got the valve timing right.

Is it firing on all cylinders? Have you pulled the spark plugs to see if any of them indicate a dead cylinder? All six fuel injectors firing?

My experience with these is that fuel pressure should be pretty steady, and should vary smoothly as vacuum changes. If you disconnect and plug the vacuum line to the FPR, does the fuel pressure still bounce around a lot? How about if you ground the fuel pump test lead KOEO?
 
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Joes4x4Ranger

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All cyl are firing. Timing is at 10* before just where it should be. I will have to have a shop check out the fuel pressure. A fuel press gauge is one tool I don't have.
 
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wood1

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I know you say you don't have a vacuum leak, but it sure sounds like one. tbars4 suggested you check the purge valve, it allows the engine to suck the fuel vapours into the intake to burn them at start-up. The charcoal canister stores the vapours, trace the vacuum line from that. If it was stuck open it would be a big vaccuum leak.

Can you borrow another mass air sensor to try? If the idle was stable while it was unplugged could that be the problem?

I feel your frustration dude. Hang in there...
 
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Joes4x4Ranger

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I know you say you don't have a vacuum leak, but it sure sounds like one. tbars4 suggested you check the purge valve, it allows the engine to suck the fuel vapours into the intake to burn them at start-up. The charcoal canister stores the vapours, trace the vacuum line from that. If it was stuck open it would be a big vaccuum leak.

Can you borrow another mass air sensor to try? If the idle was stable while it was unplugged could that be the problem?

I feel your frustration dude. Hang in there...

I'll look around the FS forum to see if someone has a MAF they will part with cheap. I will cap the vacuum fitting at the T-Body to eliminate the purge possibility. I'm bangin my head against the wall.:banghead: I've noticed the idle is much worse at hot start up. When cold it's up (the idle) around 1000 and fairly steady. As it warms up it goes down to 500-600 and starts to shake slightly and "roll" 50-75 RPM. When I start it hot, it REALLY runs like shit, till I goose the throttle a couple times then is smooths out a little.

I now have about 50 miles on the engine and 10-15 "Start Cycles". Something else strange, when I turn on the A/C the Idle speed stays around 600. It drops for a split second and goes back to 600ish RPM. Every carburated rig I ever owned had a solenoid that bumped the idle up 200-300RPM when the A/C was turned on.
 
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Tbars4

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...I was going to ask you about your A/C...You might even have a vacuum leak up under the dash...:dunno:
 
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Joes4x4Ranger

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What about the "Cold Air" Intake I have on this thing? It was on it when I got the rig last year. It has a chrome 2.5" ID metal tube and an Airrade cone filter. The intake gets hotter than F##K after 5-10 minutes of running. Could this HOT air intake be causing all the problems?
 
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Tbars4

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...It could be...I'm not sure why it's getting so hot though..:scratch:..Hook up your stock intake and see what happens..
 
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Joes4x4Ranger

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It's made of thin sheet metal, The outside air temp is 115*. Under the hood is hotter yet. The hack that owned the rig before me, is probably using the stock intake system as a bong. I have no clue where the stock intake is. Carfax says I'm the 5th owner.
 
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TedJ

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LMAO trying to imagine some guy using a intake as a bong.... anyway

Are you sure there are no air leaks in that intake? No open holes or bad clamps? Did you forget any vacuum hoses anywhere on the engine including that one under the throttle body? On the vacuum tree, maybe try pulling each line off and plugging the port to see if it runs better then, if it does look for a vac leak in that system.

How's your PCV valve?
 
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410Fortune

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did anyone suggest the IAC?
Fuel filter should be changed, especially if the truck sat for a bit while getting new parts

check for vacuum leaks around the intake upper plenum to lower intake gaskets

what plugs are you running and are they GAPPED?

check fuel pressure

you said it idled like this before, usually that means one of the parts that is still on the truck is an issue
 
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Joes4x4Ranger

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LMAO trying to imagine some guy using a intake as a bong.... anyway

Yea he could stick his whole face in it to take a hit, the filter box would be a GIANT bowl. He'd be way too stoned and busy, keeping that thing lit to fix a car right.

PCV is new, new Motorcraft Plugs, gaped at .052", IAC was replaced last year and THOUROGHLY cleaned before reinstalling. I tried the purge valve thing, no difference. The cold air intake does not appear to have any leaks. I pulled the vacuum tree completely off and plugged hole with pipe plug, no change. I know the problem is one of the original parts. I'm just so F*****G broke from the long block I cant just throw more high dollar parts at it. Every F*****G sensor, switch, module ect on this bastard start at $100. I'm broke.
 
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Joes4x4Ranger

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I did more screwing around, and just for shits and grins, I pulled the PCV out of the valve cover grommet. The idle did not change, I held my finger over the hole at the bottom of the PCV, still no change in idle WTF? I pinched the hose from the Intake tube to the oil filler cap and the idle was smoother.

Pulling the PCV should kill the motor correct? It is a big vacuum leak if not working correctly.

When I swapped the sheet metal over, the driver side valve Cover was rusted BIG TIME around the sealing surface. I filled it with a shit load of Ultra Black Gasket Maker. No oil leak, but could it be leaking vacuum? What other gaskets my be suspect in the PCV System.
 
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mshuler009

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I know you said you check the MAF but if you unplug it that sets the PCM to a default value for incoming air amounts. So if it's running bad with it in, but runs good on default values, it's probably the MAF. Another thing to check if it's missing on 1-6 is to listen to it run for about 30 seconds. Shut the truck off and pull cyl 1 plug wire off the coil pack and start truck. Repeat this going from 1 to 2 to 3...etc...until you hear a change in the engine's running. If you hear no change, then it's not something limited to one cyl. Good luck!
 
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Tbars4

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...And the spark plug gap is .054...;)
 
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