1989 Ranger 2.9L v6 rough idle at stops and slow speeds

[dungle262]

I'm having problems with my 2.9L v6 ranger idling at stops and low speeds, this is my first truck and I barely know anything about engines. Once it's warned up in cold or warm conditions it tends to surge and shake very aggressively. the shake happens on every low end of the idle fluctuations and feels the same as turning your car off and the engine jolts. at first Start its fine sitting at 1600-1700rpms and once warmed it sits at 900rpm to which the surging starts. this was just and old farm truck before me and only has 139k miles on it. So far I've replaced the IAC valve with a motorcraft one and same with the fuel filter(also motorcraft). I replaced the MAP sensor a few days ago and that's when the shaking got more aggressive. I'm just trying to learn and be able to fix this issue bc I believe she's got alot of life left in her I just need to fix this surging. I used to have a problem where after getting home from work when I shifted into park the engine would bog down and die. this issue randomly disappeared but the surging has always been there, the surging has actually gotten worse sense then. I've seen threads suggesting vacuum leaks and possibly clogged injectors, when I first had the truck it was sitting awhile so I put 1 and 1/2 bottoms of seafoam through it to getting going again(split between 3 different gas fill ups). I'm just hoping for suggestions at this point, thanks. (edit, I tried posting videos but it's saying the file size is too big)

 

[franklin2]

You could try pulling the codes to see if you get any. Also, when it's completely warmed up and idling at 900 rpm, what happens when you unplug the idle air control valve wiring plug?

 

[dungle262]

You could try pulling the codes to see if you get any. Also, when it's completely warmed up and idling at 900 rpm, what happens when you unplug the idle air control valve wiring plug?

I haven't tried unplugging the valve wiring yet and I would have to borrow a code reader which I can do this weekend. it's yet to bog down and die while I'm driving it as my daily to work. work isn't far so I'm not putting too much stress on it. I can try unplugging the valve and get back to you on that

 

[rusty ol ranger]

I haven't tried unplugging the valve wiring yet and I would have to borrow a code reader which I can do this weekend. it's yet to bog down and die while I'm driving it as my daily to work. work isn't far so I'm not putting too much stress on it. I can try unplugging the valve and get back to you on that

900 is a bit high. Should be around 650-700 IIRC.

its probably the IAC or a vacuum leak....also to pull codes you need a tester capable of reading EEC IV codes, an OBD 2 tester for modern cars wont work. You can buy an EEC IV tester on amazon or autozone for around 30 bucks

 

[gaz]

You can also pull codes without a reader using the key-on key-off sequence.

 

[dungle262]

900 is a bit high. Should be around 650-700 IIRC.

its probably the IAC or a vacuum leak....also to pull codes you need a tester capable of reading EEC IV codes, an OBD 2 tester for modern cars wont work. You can buy an EEC IV tester on amazon or autozone for around 30 bucks

I recently replaced the IAC with a motorcraft one and nothing changed. do you recommend a different brand or possibly a faulty valve. I have a buddy who has one so I will do it this weekend when I'm able.

 

[rusty ol ranger]

I recently replaced the IAC with a motorcraft one and nothing changed. do you recommend a different brand or possibly a faulty valve. I have a buddy who has one so I will do it this weekend when I'm able.

If you replaced it with a motorcraft youre probably fine there.

Pull the codes and go from there. The upper intake manifold gaskets like to leak on 2.9s, after that id be looking at the EGR valve/gaskets. Check your vacuum lines good too.

Get some starting fluid or carb cleaner and spray around where gaskets are, see if the engine revs or stalls, if it does you found your leak.

One other thing thats often overlooked is the vacuum hose running from the manifold to the MAP sensor (passenger side firewall right up top), not only will air get sucked in and screw with shit the MAP will get confused and compound things. Check this by removing and putting your finger tight on one side and blowing in the other. If your mouth loses pressure the lines bad.

It could possibly be the MAP itself but that *should* toss a code.

EDIT...
Just seen you changed the MAP and it got worse. Check the vacuum hose going to it.

Also if you have an 88-92 2.9 you wont have an EGR and can disregard that check.

 

[dungle262]

If you replaced it with a motorcraft youre probably fine there.

Pull the codes and go from there. The upper intake manifold gaskets like to leak on 2.9s, after that id be looking at the EGR valve/gaskets. Check your vacuum lines good too.

Get some starting fluid or carb cleaner and spray around where gaskets are, see if the engine revs or stalls, if it does you found your leak.

One other thing thats often overlooked is the vacuum hose running from the manifold to the MAP sensor (passenger side firewall right up top), not only will air get sucked in and screw with shit the MAP will get confused and compound things. Check this by removing and putting your finger tight on one side and blowing in the other. If your mouth loses pressure the lines bad.

It could possibly be the MAP itself but that *should* toss a code.

EDIT...
Just seen you changed the MAP and it got worse. Check the vacuum hose going to it.

Also if you have an 88-92 2.9 you wont have an EGR and can disregard that check.

in order to check the hose I need to remove it. I can pull it off of the map sensor but where it's connected to the efi system it's a big ol bolt, do I need to remove the bolt in order to check it. could it also potentially be the line that's connecting my IAC hose and my airbox? I opted 2 pictures with it to help explain. if I do need to remove that bolt I'll have to wait for it to cool down
(edit) I forgot to mention that the surging progressively gets worse the longer I sit ar idle, if I shift into park it'll calm and settle for a split second and then start surging and gets worse the longer I sit.

 

[dungle262]

https://linksharing.samsungcloud.com/6FdXfHYhEovl
idk if that link will work but if it does thats the video showing my rpm gauge surging. I don't how else to post videos bc this website claims my file sizes are too big.

 

[franklin2]

If you unplug the IAC valve, the engine should slow and may even die. If it keeps on running at basically 900 rpm, the surging may be the computer trying to control the idle, but each time it does, the idle gets higher, not lower where it wants it.

If this is the scenario, then you could have a vacuum leak, or someone may have simply adjust the throttle stop to far open. That would also most likely put your TPS voltage higher than 1 volt, which takes the computer out of idle strategy and it thinks it's running down the road, which could cause the surging also. If you wanted to check your TPS voltage with the throttle closed, you could see if it is over 1 volt, which is a problem.

 

[dungle262]

If you unplug the IAC valve, the engine should slow and may even die. If it keeps on running at basically 900 rpm, the surging may be the computer trying to control the idle, but each time it does, the idle gets higher, not lower where it wants it.

If this is the scenario, then you could have a vacuum leak, or someone may have simply adjust the throttle stop to far open. That would also most likely put your TPS voltage higher than 1 volt, which takes the computer out of idle strategy and it thinks it's running down the road, which could cause the surging also. If you wanted to check your TPS voltage with the throttle closed, you could see if it is over 1 volt, which is a problem.

I've noticed that the air box isn't connected properly, one of the bolts stripped out from previous owner. there's too vacuum lines that lead into it and one of which lead directly into the same fitting as the map sensor. it seems as if they share this fitting to create vacuum but idk. but could my airbox not holding vacuum be the potential problem sense I also have lines that connect the airbox and map sensor vacuum line together?

 

[rusty ol ranger]

I've noticed that the air box isn't connected properly, one of the bolts stripped out from previous owner. there's too vacuum lines that lead into it and one of which lead directly into the same fitting as the map sensor. it seems as if they share this fitting to create vacuum but idk. but could my airbox not holding vacuum be the potential problem sense I also have lines that connect the airbox and map sensor vacuum line together?

The airbox having a stripped bolt wont affect anything.

The "big ol nut" you speak of is just a screw in port for vacuum...just pull the rubber MAP hose off it.

What year is your truck? On my 87 those 2 little plastic red and green hoses run to the vacuum solenoid that run the EGR. On a 88-92 without EGR im not sure what they do

 

[franklin2]

I've noticed that the air box isn't connected properly, one of the bolts stripped out from previous owner. there's too vacuum lines that lead into it and one of which lead directly into the same fitting as the map sensor. it seems as if they share this fitting to create vacuum but idk. but could my airbox not holding vacuum be the potential problem sense I also have lines that connect the airbox and map sensor vacuum line together?

I think what you are looking at is the vacuum reservoir that is a vacuum storage tank. It fits underneath the air filter box. Some of the vacuum doo dads are fed from this storage tank so they still work when you are pulling a hill and the engine doesn't have any vacuum.

 

[dungle262]

The airbox having a stripped bolt wont affect anything.

The "big ol nut" you speak of is just a screw in port for vacuum...just pull the rubber MAP hose off it.

What year is your truck? On my 87 those 2 little plastic red and green hoses run to the vacuum solenoid that run the EGR. On a 88-92 without EGR im not sure what they do

this is a 1989 ranger