97 stumbling at idle

[Mat Rich]

I have a 97 Ranger with a 4.0. It sometimes bogs down or stumbles at idle.
It likes to do this sitting at a light or stop sign. It will run fine going down the road or with my foot on the gas when it starts to behave this way. Sometimes but not every time after stopping the rpms will suddenly drop to about 500 or lower than recover it may do this a couple of times than run good,go dead sometimes or just continue acting up Sometimes it will lope after driving it a bit and putting it in park. Sometimes it seems to idle at about 800 sometimes a little higher and also the gas mileage could be better.

I retrieved lean codes 0171 0174 and egr code 0401, it has threw a 0153 in the past but it has not come back yet. I have read multiple posts on here ,other forums and sites on what the problem might be. But with multiple causes i think i can use some advice. Also i just have plain code reader so i am not able to get any additional data

It has new plugs and wires,fuel filter less than a year old, air filter not dirty,cleaned the maff with maff cleaner, also cleaned the iac Checked for vacuum leaks but could not find any including putting a vacuum gauge on it and got 20-22 at idle but of course it decided not to act up with the gauge attached. I also checked the egr valve for proper operation and to see if it would hold vacuum it seemed to be ok. The Dpfe ports were clogged i cleaned them i suspect the sensor is bad and will replace it sometimes but don't think it is what is causing it to run this way

After reading a TSB about the fuel rail gaskets on 97s i am suspecting this but again i am asking for second opinions

If it is possibly the fuel rail gasket would you recommend replacing the lower intake gasket too.

If so what do think about these sets
Victor Reinz MIS19316 or Fel-Pro MS98005T

Also I have read different opinions about the 2 piece vs the one piece lower intake gasket anybody know which one is really better.

The Last Couple trips I drove it
1. I let it warm up a while, it idled good than started bogging down in the yard. I turned it off than re-cranked it and drove it about 5 miles than come back home then went to town which is about 10 miles it run fine at all the lights it acted up on time in the parking lot of a store when I had to stop behind a vehicle

2 On a short trip drove it about a mile it acted up and went dead when i stopped at a sign I Cranked it back up and went on

3.Today I let it warm up about a while before i pulled out, drove about a mile than it acted up and went dead at same stop sign I cranked it back up went on to town about 10 miles it run good, On the way back it acted up at a light but i kept my foot on the gas than it run fine. Also when I was stopped in a turning lane and having to wait a while it started acting up but this time i put it in park it i maintained idle speed but run a little rough

Thanks and grateful for any help

Mat

 

[RonD]

It reads like it only stumbles when in Closed Loop, after it warms up.

When you start a computer controlled engine, the computer is in Open Loop.
If engine is cold computer will set idle higher, 1,000, and run fuel richer, it ignores O2 sensors, computer is running engine from data tables in memory.
When engine warms up idle will go down to 750 and computer goes into Closed loop, computer now uses all sensors and calculates fuel mixture based on MAF data about air flow and O2 sensor data about Oxygen in the exhaust.

Idle is controlled by the IAC valve, computer lets in more air to raise idle and less air to lower idle, using this valve.
This valve can get dirty and stick a bit, computer tries to correct RPMs but you end up with an up and down battle since IAC valve isn't responding as it should.
Easy to clean these.

EGR valve was checked but did you remove it and clean it.
This valve can also get dirty and stick open a bit which lowers idle and the computer struggles to stabilize it.
Put a longer vacuum line on the EGR valve and start warmed up engine, suck on the vacuum line to open EGR valve a bit, and see if that causes the same issues you are seeing.


You may what to see if you can borrow a Live OBD II scanner, then watch the O2 sensor data when you come to a stop, it doesn't sound like an O2 sensor issue, but..............if fits with closed loop

 

[Mat Rich]

I did the clean the IAC with little to no improvement. However I did not clean the egr valve which I will do.

 

[RonD]

Also check the PCV Valve and it's hose.

The PCV valve opens at higher RPMs(lower vacuum) then closes at lower RPMs(higher vacuum), so at idle it should be sucking only a little air, if the valve inside isn't holding it could cause lean codes and stumbling idle.

 

[Mat Rich]

The pcv hose is in pretty good shape with no splits or dry rot. I found it fits snug on the intake but a little loose on the pcv valve. I used a zip tie as a clamp to make it fit a little more snug. I also tested the pcv valve the only way I know by putting my finger over it and it would close and produce a strong suction. I previously had replaced it not so long ago (metal version) but after the truck started acting up I Cleaned and replaced it with the old one (plastic motorcraft) yet seen no difference I put the newer one back on today along with the ziptied hose. The grommet on the valve cover seems to be ok too.

I got a gasket today so I could clean the egr valve. I found out I did not have the right size wrench to disconnect the exhaust manifold line from the egr and also that it is very tight and rusted on there. So I don't want to miss nothing up especially that egr intake hose. So I have decided to spray penetrating oil (PB Blaster) on it than drive it and keep up the process until I get the right size wrench (hopefully sometimes next week) which I believe is a 27mm anybody out there know for sure?

Thank you for your suggestions as you may have figured out I am no mechanic but I don't like throwing parts at one and hoping it fixes it. Just trying to learn a little more as I go along