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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

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Old 09-23-2009, 05:35 AM   #1
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Rough Idle When Warm (3VZE)

94' 3VZE Automatic.

On a cold start, 4runner idles and runs fine (between 1000-1200 RPMS). When the truck warms up it will idle around ~500-750RPMS but sputter, almost like a miss, when the truck is warm it takes a bit for it to crank over. I do have a CEL for Engine Code 25. I also had to set the BISS pretty far out for it to idle correctly.

Stuff I have done:
-EGR Block Off
-NGK Spark Plug Wires
-NGK V-power Spark Plugs (gapped 0.32)
-Seafoam Treatment
-Fuel Injector Cleaner Treatment

Replaced:
- o2 Sensor
- Fuel Filter
- Intake Filter
- TPS
- VAFM
- Exhaust from header pipe back (including upgrading to a high-flow cat)
- Coolant Temp Sensor
- TVV

I ran a unlit MAP torch all around the vacuum areas and intake manifold as well with no idle change. I read somewhere that something in the throttle body gets super gunked up that would cause these symptoms. Going to look at that but any other info would be greatly appreciated. I am thinking this may be something fuel related (fuel pressure regulator?), but I don't have a fuel pressure kit to test it.
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Old 09-23-2009, 10:02 AM   #2
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Idle bypass plugged? maybe TPS sensor bad or moved?
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Old 09-23-2009, 11:06 AM   #3
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Quote:
Originally Posted by 88toyblackjack View Post
Idle bypass plugged? maybe TPS sensor bad or moved?
I replaced the TPS and re-checked it a couple weeks ago. All within spec (also did the allen head screw kit) and it has not moved. Will tear the throttle body off tonight and check to see if that's plugged up.
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Old 09-23-2009, 01:45 PM   #4
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Clogged cat?
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Old 09-23-2009, 04:46 PM   #5
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Quote:
Originally Posted by sb5walker View Post
Clogged cat?
In my original post:
- Exhaust from header pipe back (including upgrading to a high-flow cat)

Brand new cat, doubt it's clogged.
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Old 09-24-2009, 01:38 PM   #6
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BUMP for any other suggestions.
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Old 09-25-2009, 10:54 AM   #7
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kind of experiencing the same symptoms as you, will monitor this thread. i'm pretty sure my TPS needs to be adjusted but would like to know what the other possibilities are.
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Old 09-27-2009, 06:56 AM   #8
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It's been raining here so I have been unable to check things out. I have also noticed that if I am cruising and I lightly had my foot on the pedal (steady) the RPMS will start to bounce up and down. I checked my grounding cable and have even shaked the wiring harness with no change.
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Old 09-27-2009, 07:32 AM   #9
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TPS, EGR, distributor, fuel pressure, vacuum leak, injectors. Check in that order for solutions to your symptom. Any codes stored?
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Old 09-27-2009, 07:14 PM   #10
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Quote:
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TPS, EGR, distributor, fuel pressure, vacuum leak, injectors. Check in that order for solutions to your symptom. Any codes stored?
New TPS and adjusted correctly (checked 3x)
EGR is blocked off
Vac Leak I used an unlit MAP torch all around the engine bay with no idle change
Fuel Pressure - I don't have a tester
Injectors - been raining all week so have not been able to work on it. Would need to take off the intake plenum to even get to the injector clips, correct?

Engine code 25

Does anyone read my OP?
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Old 09-27-2009, 07:24 PM   #11
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You do realize that idle and timing are set with the engine warmed up? Get it to run right warmed up and then troubleshoot the cold start issues.

and it seems you still have that hidden vacuum leak you never found, right? ... considering that code 25 - a/f ratio lean.
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Old 09-27-2009, 07:46 PM   #12
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Quote:
Originally Posted by abecedarian View Post
You do realize that idle and timing are set with the engine warmed up? Get it to run right warmed up and then troubleshoot the cold start issues.

and it seems you still have that hidden vacuum leak you never found, right? ... considering that code 25 - a/f ratio lean.
Yes, I did most of my testing when the engine was warmed up. The idle seems to be fine it's just that miss/shake that only comes around when the car is warmed up. I don't have a cold start issue?
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Old 09-27-2009, 08:02 PM   #13
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Okay. You've checked valve clearances? You've had the injectors flow-checked / cleaned / balanced? You said 5mm plug wires... I'm hoping you meant 8 or 9 mm wires. No exhaust leaks, right? Compression is relatively consistant between cylinders?
O2 is heated and you've verified that the heater element is working? O2 sensor itself is oscillating properly per FSM specs?

Your code 25 suggests that the ECU has run out of room to compensate for what it sees as a lean mixture- it can't add any extra fuel. One possibility is that the ECU thinks the engine is colder than it is so it needs more fuel. You've changed the CTS so that should eliminate that. Exhaust leaks between the engine and O2 can cause lean readings. I'm guessing you've checked and fixed those. PAIR system is working when it should, and not working when it shouldn't? EGR blocked can 'amplify' mixture readings to a point but they would trend toward rich, not lean.
No leaks in the duct to the air filter, right? They may not show up using MAPP gas itself since they are relatively low vacuum points so maybe massage the joints while spraying the MAPP, trying to expose cracks / leaks mechanically speaking. Overall, maybe try that everywhere- move hoses around while you spray the gas (okay, that doesn't sound right but maybe if you sent me pics, I could clarify...). Likewise, try having someone hold the gas pedal down 1/4-1/2 way or whatever while you move the gas source around. Some vacuum sources only operate at particular throttle positions.

Start thinking like an engine and smog control.
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Old 09-27-2009, 08:28 PM   #14
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It's a brand new Denso O2 sensor. I swapped to NGK spark plug wires a month or so ago I fixed that in my first post. What I am not getting is why the ECU would read a "lean" mixture when my exhaust tip is black which is a sign of it being a rich condition.

As for valve clearance and checking the injector I have not pulled the intake plenum or valve covers off so those have not been checked.

Compression test is next on the list.
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Old 10-02-2009, 10:37 AM   #15
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Cold Start Injector - 3.5 Ohms (so that checks out)

I doubled checked the NGK wires, they are 8MM. Also ran the MAP gas again and massaged the lines/according/joints of all the hoses and the intake. No change, I was considering blocking off the PAIR Reed Valve system. The less sources of a vacuum leak the better, plus this isn't a DD for me. I am emission exempt in my state since I drive >5,000 miles/per year.

I also checked the piece on the throttle body and it was pretty clean (see pictures):
Click the image to open in full size.
Click the image to open in full size.


Also, what is this? I keep putting vacuum caps on it but they keep splitting! I am sure it's not helping my problem that this is split.
Click the image to open in full size.


This is what I see coming from my exhaust as well, I didn't think running in a "lean" condition would cause this.
Click the image to open in full size.


P.S.S - Is my ground wire to chassis thick enough? Seems a bit small....
Click the image to open in full size.
Click the image to open in full size.

I guess my next step is a compression check? I will also pull off the exhaust manifold shields and check to make sure there are not any exhaust leaks there. If I ran the unlit MAP torch around that area would it work the same (rev high if there is a leak) like the vacuum leaks?
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Old 10-05-2009, 10:13 AM   #16
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Bumping it up.
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Old 10-05-2009, 02:54 PM   #17
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If you haven't done so already, get some B12 with the little straw sprayer and clean out the throttle body and especially concentrate on the idle air circuit. It's one of the holes towards the bottom of the throttle body near the opening that connects to the air intake hose. If this is clogged or gummed up with carbon buildup, it can cause a rough idle. Hope that helps....

Afterthought.... if you haven't checked valve clearances, you need to do that. Tight exhaust valves will contribute to this problem as well. I just went through the classic "rough idle" with a 1994 SR5 V6 I just bought (185K miles). I adjusted the valves, thoroughly cleaned the gunk out of the plenum and throttle body with B12 and put in a new plenum gasket and throttle body gasket. Ran like a charm when done and idled perfectly. Your idle issue could possibly be caused in part by a leaky plenum and/or throttle body gasket which could explain your code "25" (too lean mixture if I recall correctly as a result of sucking extra air through an intake leak).

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Old 10-06-2009, 08:26 AM   #18
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Does your engine run rich when it idles rough?

I recently had a similar problem. The engine started fine cold and ran ok until it warmed up. Once it warmed up and idled down, it would barely hold idle and the exhaust was super rich. It turned out to be the cold start injector, even though that checked out as ok with the Ohm meter.

A Toyota mechanic for a local dealer guestimated that the cold start injector was the culprit over the telephone! He suggested the following test to confirm:

Pull the cold start injector from the plenum, but leave the electrical conector in place, and place it in a jar.

Have a friend start the engine while you watch the injector. It should spray briefly then shut off. If it continues to drip or seep or spray, it is bad.

The bad news is that Toyota wanted $190 for a new one. Solved the problem right away though and it was an EASY repair.

Good luck,

WJ

Last edited by Wrenchinjoe; 10-06-2009 at 08:39 AM.
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Old 10-06-2009, 09:13 AM   #19
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Quote:
Originally Posted by RockMtn4Runner View Post
If you haven't done so already, get some B12 with the little straw sprayer and clean out the throttle body and especially concentrate on the idle air circuit. It's one of the holes towards the bottom of the throttle body near the opening that connects to the air intake hose. If this is clogged or gummed up with carbon buildup, it can cause a rough idle. Hope that helps....

Afterthought.... if you haven't checked valve clearances, you need to do that. Tight exhaust valves will contribute to this problem as well. I just went through the classic "rough idle" with a 1994 SR5 V6 I just bought (185K miles). I adjusted the valves, thoroughly cleaned the gunk out of the plenum and throttle body with B12 and put in a new plenum gasket and throttle body gasket. Ran like a charm when done and idled perfectly. Your idle issue could possibly be caused in part by a leaky plenum and/or throttle body gasket which could explain your code "25" (too lean mixture if I recall correctly as a result of sucking extra air through an intake leak).
When I had the TB off to check that port on the bottom I cleaned the TB and the opening of the plenum. I may take the plenum off to do a valve cover gasket replacement/PCV soon though. Will try cleaning it out and replacing those gaskets as well. Would you know the name of that rubber-type cap is on the TB line in my picture above?

Quote:
Originally Posted by Wrenchinjoe View Post
Does your engine run rich when it idles rough?

I recently had a similar problem. The engine started fine cold and ran ok until it warmed up. Once it warmed up and idled down, it would barely hold idle and the exhaust was super rich. It turned out to be the cold start injector, even though that checked out as ok with the Ohm meter.

A Toyota mechanic for a local dealer guestimated that the cold start injector was the culprit over the telephone! He suggested the following test to confirm:

Pull the cold start injector from the plenum, but leave the electrical conector in place, and place it in a jar.

Have a friend start the engine while you watch the injector. It should spray briefly then shut off. If it continues to drip or seep or spray, it is bad.

The bad news is that Toyota wanted $190 for a new one. Solved the problem right away though and it was an EASY repair.

Good luck,

WJ
Yes, it does run rich when it's idling rough! I was looking at that and saw it has a gasket. If I were to do this test would I need to replace that gasket or could I get away with re-using the old one? Not sure what th material is paper, o-ring type etc.
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Old 10-06-2009, 10:14 AM   #20
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I think you would be ok to reuse that gasket, assuming the injector comes out cleanly and does not damage the old one. (I pulled my plenum last summer and reused that gasket after reassembly. Just be sure to check that it doesn't leak when you reassemble.)

However, if the cold start injector is your problem as it was for me, the new part comes with a new gasket and new banjo washers for the fuel line.

Hope this solves your probelm. I scratched my head for weeks trying to diagnose the problem, but it took less than 10 minutes to fix.

Good luck,

WJ

Last edited by Wrenchinjoe; 10-06-2009 at 12:40 PM.
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