93 V6 Rough Idle

[fjcruiserpd]

93 V6 Automatic 167,000 miles. Second owner. Purchased in December 2013.

My truck has a bit of an intermittent shake when either in park or stopped at a light/stop sign almost as if it is going to stall but never does. And lately it has been hesitating a bit at acceleration from stop and just driving rougher than normal. Before all of this it was a smooth ride for most of the time.

I'm sure there a various things that could be going on, but I'm not much of a mechanic so if I could get an idea on where to start in terms of diagnosis that would be great. I'm good at fixing/replacing what is broken, just need to know how to find the problem.

 

[77'911]

If it has never had the motor mounts done in 167k, you might consider replacing them. I would start there and then work your way to detonation quality(state of tune, fueling, etc..). Best of luck with it.
regards

 

[giro]

Have you been through a few tanks of gas while having this issue?

Does it happen when in Park, or only when stopped with the brake on? All the time, or just at night?

If the non-stopped issues aren't that bad, I'd probably just look at bumping up the idle a tiny bit. On some cars the brake lights are enough to cause a little roughness, or maybe that combined with the brakes trying to stop while the car is trying to go.

But roughness at other times might point somewhere else. If the air filter is good, you might consider replacing the fuel filter. I've never done it on my 4runner, but have had to occasionally on older non-toyota cars.

 

[bills86e]

Buy some CRC throttle body cleaner and clean it, the IAC, Modulator filter, MAF, and adjust the idle screw on throttle body to 750-850 rpms at idle.
If you pull the rubber hose off the EGR valve and it smooths out, you may have to look at the vacuum hose routeing diagram thats on driver side under the hood, to confirm each hose connection tube tubes are correct.

 

[fjcruiserpd]

Have you been through a few tanks of gas while having this issue?

Does it happen when in Park, or only when stopped with the brake on? All the time, or just at night?

If the non-stopped issues aren't that bad, I'd probably just look at bumping up the idle a tiny bit. On some cars the brake lights are enough to cause a little roughness, or maybe that combined with the brakes trying to stop while the car is trying to go.

But roughness at other times might point somewhere else. If the air filter is good, you might consider replacing the fuel filter. I've never done it on my 4runner, but have had to occasionally on older non-toyota cars.

I believe this issue started with the current tank of gas.

It happens when it park as well no matter the time of day.

It already idles at around 850, should it be more?

What exactly constitutes a "good" air filter. I've checked it a few times and it never really looks dirty.

Also, to give some insight as to what I'm experiencing; when stopped at a light (or parked) the car will idle smooth for a few seconds and then give a little shake. It pretty much follows this pattern constantly.

 

[fjcruiserpd]

Buy some CRC throttle body cleaner and clean it, the IAC, Modulator filter, MAF, and adjust the idle screw on throttle body to 750-850 rpms at idle.
If you pull the rubber hose off the EGR valve and it smooths out, you may have to look at the vacuum hose routeing diagram thats on driver side under the hood, to confirm each hose connection tube tubes are correct.

I cleaned the throttle body a few weeks ago just because. I'll look into the other things as well.

FWIW I just ran some Seafoam through it. I'll report back to see if anything changed.

 

[541joseph]

I believe this issue started with the current tank of gas.

It happens when it park as well no matter the time of day.

It already idles at around 850, should it be more?

What exactly constitutes a "good" air filter. I've checked it a few times and it never really looks dirty.

Also, to give some insight as to what I'm experiencing; when stopped at a light (or parked) the car will idle smooth for a few seconds and then give a little shake. It pretty much follows this pattern constantly.

Drop the air filter on the ground dirty side down and if dirt falls off it needs replaced

 

[fjcruiserpd]

Well I drove it this evening and it drove terribly. Felt as though at any moment while I was on the highway that it would die on me. Then as soon as I pulled into my driveway the check engine light came on.

I lifted the hood and could hear what sort of sounded like air being pushed in (or out) but no place to go. Definitely not a sound I've heard before.

Hopefully whatever codes I can pull will give me some insight...

 

[Jdrum1]

Vacuum line come loose?

 

[fjcruiserpd]

Vacuum line come loose?

Just checked. Didn't see any lines that weren't connected to anything. And they all appeared to be routed to the corrected places.

Just a question: Would a bad or dead O2 sensor affect idle and drive quality? Not saying this is my diagnosed problem just wondering.

 

[Orion_71115]

Yes it will.

 

[bills86e]

IAC or fuel pump, could be culpret.
Open the diagnostic port cover and look for T1 and E. jumper those then turn ignition to the ON position and watch for the DTC readings. Search the codes, fix what the code symptoms suggest is wrong.

 

[541joseph]

Just checked. Didn't see any lines that weren't connected to anything. And they all appeared to be routed to the corrected places.

Just a question: Would a bad or dead O2 sensor affect idle and drive quality? Not saying this is my diagnosed problem just wondering.

Typically a bad o2 sensor won't cause this issue until after damage from running improperly is already caused

 

[fjcruiserpd]

Okay, so I'm going to check for codes either today or tomorrow. But I have questions.

I'm not a mechanic like I said, so I need some help getting the codes. I'm reading everywhere to use a jumper to find the codes. What is this jumper and where can I buy it? Is this the only way to pull codes? Is there a scanner like with newer OBDII enabled vehicles that will just show me the codes instead of me having to count engine light blinks?

Also, with these blinks - say the code is something like 85, does that mean I have to sit there and count 85 blinks? Or does it blink 8 times, pause and then blink 5 times?

 

[541joseph]

Okay, so I'm going to check for codes either today or tomorrow. But I have questions.

I'm not a mechanic like I said, so I need some help getting the codes. I'm reading everywhere to use a jumper to find the codes. What is this jumper and where can I buy it? Is this the only way to pull codes? Is there a scanner like with newer OBDII enabled vehicles that will just show me the codes instead of me having to count engine light blinks?

Also, with these blinks - say the code is something like 85, does that mean I have to sit there and count 85 blinks? Or does it blink 8 times, pause and then blink 5 times?

Yes there are scanners that do it. Snap-on's modis scanners do it and simmilar high end ones will but we are talking thousands just take any wire laying around jump the ports. If its 85 it will blink 8 times then pause for a second and the do 5

 

[giro]

I lifted the hood and could hear what sort of sounded like air being pushed in (or out) but no place to go. Definitely not a sound I've heard before.

On a 3000gt I worked on for a bit, I had a sound I was tracking down for a bit. It turned out the throttle body gasket was leaking. It probably just needed to be seated right, but a new one was only $3 or so, so I replaced it. It was a pain to get just right, but once I did that particular noise went away.

I was going to mention this either way, but then I saw you said you just cleaned your throttle body. Hmmmmm

Either way, try to figure out where that sound is coming from. Basically if air is leaking in or out of the system somewhere after the MAF, then the MAF isn't reporting the right amount of air that's actually making it into the engine, and so the air/fuel mixture gets all screwed up and it can run terribly.

(on that 3000gt the first time I tried to drive it home I downshifted and an intercooler line came off. It wouldn't run after that, and had to get towed. It was a simple problem.....once you figured it out)

BTW, I haven't tried it on my 4runner, but often you can unplug the MAF and be in 'limp home' mode. It won't run great, but it should run as it would use the default settings instead of basing fuel off of your sensors. Turned out this was a common trick on the much more problematic 3000gt's.

 

[fjcruiserpd]

On a 3000gt I worked on for a bit, I had a sound I was tracking down for a bit. It turned out the throttle body gasket was leaking. It probably just needed to be seated right, but a new one was only $3 or so, so I replaced it. It was a pain to get just right, but once I did that particular noise went away.

I was going to mention this either way, but then I saw you said you just cleaned your throttle body. Hmmmmm

Either way, try to figure out where that sound is coming from. Basically if air is leaking in or out of the system somewhere after the MAF, then the MAF isn't reporting the right amount of air that's actually making it into the engine, and so the air/fuel mixture gets all screwed up and it can run terribly.

(on that 3000gt the first time I tried to drive it home I downshifted and an intercooler line came off. It wouldn't run after that, and had to get towed. It was a simple problem.....once you figured it out)

BTW, I haven't tried it on my 4runner, but often you can unplug the MAF and be in 'limp home' mode. It won't run great, but it should run as it would use the default settings instead of basing fuel off of your sensors. Turned out this was a common trick on the much more problematic 3000gt's.

Definitely somethings to think about...thanks.

Another added caveat to my situation is that today I started it up and right away started to get a fuel-like smell. Ya know, normally there will be a faint odor if I let the car run for a while, but this time it was right away and stronger than normal.

Related, probably?

I know I'm likely to have more answers once I pull the codes (will do that tomorrow) but I just wanted to add this bit of detail before I forget just in case it's helpful.

 

[giro]

today I started it up and right away started to get a fuel-like smell. Ya know, normally there will be a faint odor if I let the car run for a while, but this time it was right away and stronger than normal.

It's likely that the computer just uses the defaults at cold start. That's how that 3000gt worked, and part of why you could unplug something that mattered to have it use the defaults. On it, at an ambient temp of 70 or so, it would take maybe 6 minutes to heat up enough to switch over to the computer settings. (I assume the 4runner does the same thing.....anyone know?)

But, where is that smell of fuel? If at the tailpipe only at starting then it could have just had a little unburned gas while starting. If later on at the tailpipe, then it could be a bad mixture, but if it isn't then it could point to things like a cylinder being out. That could be as easy as a fouled plug or an injector not working, or something more.

If the fuel smell is under the hood, start at the injectors and work backwards, to the fuel rail, and then fuel filter. Any connection could cause it. I don't know what is most common, but I had a little fuel leak/smell on one of those injectors on that 3000gt.

Narrow it down a bit, but if it's at the tailpipe hopefully it will go away when you fix your main problem.

 

[fjcruiserpd]

I read around a found that I could use a paper clip to pull the codes o I just tried it and nothing happened?

Is this trick usually pretty reliable? Could something be wrong with my diagnostic port? Or is the CEL not sending any codes?

I'm really trying to at least do this initial step without having to pay someone to diagnose my problem.

 

[fjcruiserpd]

Codes: 12 and 25

Okay, I was finally able to pull the codes. I got codes 12 (Knock Control Sensor signal or RPM Signal) and 25 (Air-Fuel Ratio Lean)

Going to look them up now but if anyone has had experience with these two codes, please chime in with thoughts!

ETA: I'm assuming this is what these codes mean. I got that info from a web search. Will double check with the FSM.