'99 4 cylinder, intermittent stumbling and weak power.

[triangles]

My '99 2.7L 2wd 140K miles has developed a drivability issue. Acceleration has become weak and the engine stumbles intermittently. I also get intermittent P0133 and P0130 codes O2 malfunction and O2 slow response codes. Every once in a blue moon I get a P0505 idle air control valve malfunction. When I first start it there is a bleachy smell to the exhaust.

Steps taken so far:
-Replaced both O2 sensors and air filter.
-Had the cat. pressure tested to make sure it wasn't plugged.
-New plugs and wires. (Autolite double platinum gapped to 0.035")
-New fuel filter (replaced the PCV valve too for s&g's)
-Pressure tested fuel system; Constant 46PSI. Might have sagged a little to 45PSI on the freeway WOT. When engine shuts down the pressure bleeds down to 34PSI.
-Wiring checks out okay and the connectors are clean.

The truck seems to behave and the trouble codes above seem to indicate the engine is running lean. Nothing made any difference until I replaced the fuel filter which reduced the stumbling. The stumbling also isn't quite as repeatable now. It used to do it rather consistently around 70mph. I'm beginning to wonder if the ECU is going bad. If anyone has experienced this please let me know how you solved it!

Supposedly there is a small crack in the exhaust manifold near the downstream flange. There is no audible noise coming from here. The only way I could tell there was a slight leak was by using seafoam and seeing a little smoke come out near the flange. This manifold crack was there at least a year before any of the stumbling started and it has not gotten any worse so I doubt it is contributing to my current issue. I only mention it since I believe it may be partially responsible for the intermittent false O2 error codes which also predate the stumbling problem.

 

[Paperjam]

Woah woah on thinking the PCM is bad, have you hooked up a scanner and looked at your data stream while running? You should be checking your long term fuel trims to see if it's actually running lean. This can be caused by vac leaks, intake leaks, low fuel delivery or O2 sensor malfunctions. My 2.7 had slow response on the O2 but the engine was not getting enough fuel, you may have good fuel pressure but the pump could not be providing enough fuel VOLUME. Injectors can get plugged with gunk in the screens and cause a restriction. You can do a injector pressure drop test to check the volume. It sounds like you freed it up a bit with the filter but there could be more.

What color were the plugs when you pulled them?

Honestly check the fuel trims first, if the PCM is maxing out (trying to add) fuel while under acceleration you will have to figure out why.

A crack in the manifold that sucks air INTO the exhaust will lie to the sensor telling it the engine is too lean and will be adding fuel to compensate.

 

[Paperjam]

Also, clean your maf if it has one

 

[gamefreakgc]

You already found the problem. Fix the manifold leak with either some JB weld or remove the part to have it welded. 99% sure it will fix it.

 

[Paperjam]

Jb weld an exhaust manifold? That will just burn or flake off, manifold cracks are stress induced and welding is also a bandaid at best. Welding cast iron requires a crap ton of heat via a torch before you can even weld it with your standard mig.

 

[davidch]

Have you checked the valve clearances, or performed a compression check? In my experience, and there are plenty of testimonials to the same out there on the Internet, a 3RZ - or its kid brother the 2RZ - with that kind of mileage will have exhaust valves heading for 0 clearance. It's an oft-overlooked maintenance item.

If nothing else, check the clearances yourself. They're fairly easy to check on a 4-cylinder in that not a lot of "surgery" is needed to get to them, and an inexpensive set of feeler gauges is all you need by way of tools.

Actually adjusting the valves is another matter.

 

[Paperjam]

Have you checked the valve clearances, or performed a compression check? In my experience, and there are plenty of testimonials to the same out there on the Internet, a 3RZ - or its kid brother the 2RZ - with that kind of mileage will have exhaust valves heading for 0 clearance. It's an oft-overlooked maintenance item.

If nothing else, check the clearances yourself. They're fairly easy to check on a 4-cylinder in that not a lot of "surgery" is needed to get to them, and an inexpensive set of feeler gauges is all you need by way of tools.

Actually adjusting the valves is another matter.

Not a bad thought. A leak down is another way to check where you are losing compression (if you are) without pulling valve covers.

 

[triangles]

Have you checked the valve clearances....

That is on my to do list when warm weather gets to Ohio. I would like to thank everyone for their thougths/suggestions.

I have an update that will likely help anyone with similar issues. I finally got to the bottom of this! :rockon: It turns out I had two problems resulting in the driveability problems I described. First the Idle Air Control (IAC) valve was bad. The "close" coil was shot. This caused the weak acceleration and high idle. Second The Exhaust Gas Recirculation (EGR)system was choking the engine at cruising speeds. The valve was not stuck open but it would dump too much exhaust into the intake when it did open at cruising speeds causing severe stumbling and making it nearly impossible to keep a steady speed. I'm sure the throttle body being beyond filthy didn't help either.

I removed the throttle body and thoroughly cleaned it and replaced the IAC. Be sure to order a new gasket when you replace the IAC. For some reason it's listed as a throttle body gasket instead of an IAC gasket so it makes finding it a little more difficult. I thought a new throttle body gasket was a good idea too. There was an incredible amount of oily carbon to clean off the throttle body! When I put it all back together the idle was back to normal and my highly calibrated butt dyno says I had 2x the power for acceleration! However as soon as I reached the speed I wanted to go it would stumble much worse than before!

I already had the truck warmed up and idling perfect at 700 RPM when I started looking into the EGR. To test the EGR simply warm up the engine until it bumps down to the warm engine idle speed. Then pull the vacuum hose off the EGR valve and apply vacuum to it. If the valve is working it should almost immediately stumble and die when you apply the vacuum. I used a syringe for my "vacuum generator." I'd imagine you could just put a length of hose on it and suck it to open the EGR valve. If you suspect the EGR is causing you stumbling problems the easy way to test this is to simply undo the vacuum hose that actuates the EGR valve and cap it. This is how I tested to verify the EGR was the root of my problem. When I drove it after doing this I didn't even have a hint of stumbling, it was like driving a new truck again! Now I just have to figure out what is causing the EGR system to malfunction or just wire a 10k resistor in place of the EGR temp sensor and delete the EGR system. The resistor will fool the ECU into thinking it sees the heat (flow) of the exhaust gases so you don't get a CEL with a P0401 code.

 

[triangles]

OK so I spoke too soon. I have replaced the EGR vacuum modulator valve and all vacuum lines. Also re-enabled the EGR valve (reconnected the vacuum line). It now stumbles and struggles to exceed 30mph until it warms up. The stumbling under constant speed is also worse again.

I have a "mini header" in hand that I will prep and paint this weekend. The OEM part number for this is 17141-75080 I got it new for $182 shipped since I couldn't find a used one. Some weekend soon I will install it. Hopefully this will take care of the O2 errors. I also plan to check/adjust valve lash at the same time but I am doubtful either valve lash or a slight exhaust leak are the underlying cause. I believe the problem is somewhere with how the ECU controls ratio and the EGR smothering the engine. I'll report back after I get this done. Hopefully I am wrong and correcting the exhaust leak and valve clearances will be the solution!

 

[triangles]

I thought I had updated it here but apparently I had not. Anyway back in late April/early May I gave up trying to solve the mystery. I bent over grabbed my ankles and spelled "RUN" taking it to the dealer. I loathed taking it to the stealership but I figured it would be a waste of time to take it to a local shop that would want to just keep throwing parts at it and hope they get it right(like I had been doing). Well I think that's what the stealership did anyway. They had it for over 3 weeks and kept telling me it was this, no it is that, etc etc. If I didn't already mention above, I did adjust the valves and get the mini-header installed.

Short version: $1500, 3+ weeks at the stealership, new injectors and O2 sensors solved my problem.

Long version: They replaced my aftermarket plugs and wires even though they didn't need it since I had just replaced them. Apparently Toyota is very proud of their plug wires. Insisting the brand new Autolite wires failed their test. They insisted they had to do this before further testings. They tried swapping in a borrowed MAF to no avail. Then they were certain it was the fuel injectors so new fuel injectors. They said this greatly helped but it still stumbled. I don't know if I believe them. God knows what else they tried and didn't tell me. Then they replaced my cheap ass aftermarket oxygen sensors, I had just replaced the the originals in response to an O2 error code. I have a suspicion that the O2 sensors were the root cause and the injectors probably weren't in the best shape contributing to the issue.

 

[vincedprince]

Hello and thank you for the add. I have been trolling the forums for a while now and learning from all the information provided here. However, I have an issue that has boggled my mind and would love to get opinions from those who have more experience with this vehicle.

2000 2.7L Automatic 220K Miles -owned by my retired uncle and I'm helping him out with the car.

Last year, did some tune-up: changed plugs, ignition coils, air filter. A couple of months later, started misfiring and threw a P0301. Since I've been busy and it's his spare car, I only got a chance to take a look at it last month (shelter-in-place). So, it sat for a good 6 months unused.

The P0301 was due to a faulty ignition coil. Swapped that out with a new one and the car started right away with no problems. I left the car idling while I put air in the tires (was low since it was parked for a while).

As I got out of the driveway, stepped on it and it ran VERY VERY SLOWLY - 0-25MPH in like 6 seconds!

No codes, no misfire, no hesitation, nothing! It idles nicely with the engine purring smoothly. It took forever to get to 40MPH on a level road. Since there were no codes, I thought it was the fuel filter. I changed that but still no power at all. I don't think it's stuck brakes as it rolled smoothly down the driveway on neutral.

Anybody have encountered this kind of issue? Suggestions are greatly appreciated.

 

[HiLife]

5 year thread!
It may be just spoiled gas. I would think 6 month stored ethanol has something to do with it. Check your maf sensor, it could be dirty.
Welcome to the forum btw.

 

[UnderFire]

Hello and thank you for the add. I have been trolling the forums for a while now and learning from all the information provided here. However, I have an issue that has boggled my mind and would love to get opinions from those who have more experience with this vehicle.



2000 2.7L Automatic 220K Miles -owned by my retired uncle and I'm helping him out with the car.



Last year, did some tune-up: changed plugs, ignition coils, air filter. A couple of months later, started misfiring and threw a P0301. Since I've been busy and it's his spare car, I only got a chance to take a look at it last month (shelter-in-place). So, it sat for a good 6 months unused.



The P0301 was due to a faulty ignition coil. Swapped that out with a new one and the car started right away with no problems. I left the car idling while I put air in the tires (was low since it was parked for a while).



As I got out of the driveway, stepped on it and it ran VERY VERY SLOWLY - 0-25MPH in like 6 seconds!



No codes, no misfire, no hesitation, nothing! It idles nicely with the engine purring smoothly. It took forever to get to 40MPH on a level road. Since there were no codes, I thought it was the fuel filter. I changed that but still no power at all. I don't think it's stuck brakes as it rolled smoothly down the driveway on neutral.



Anybody have encountered this kind of issue? Suggestions are greatly appreciated.

When you're accelerating does the RPM rise higher than you feel it should or does it feel like something may be slipping, or does it feel normal as far as that goes but like the engine is bogging down?

Sent from my JSN-L23 using Tapatalk

 

[vincedprince]

5 year thread!
It may be just spoiled gas. I would think 6 month stored ethanol has something to do with it. Check your maf sensor, it could be dirty.
Welcome to the forum btw.

Thought about spoiled gas as well but I never had any experience what spoiled gas does to a car. Will try the MAF, thanks!

When you're accelerating does the RPM rise higher than you feel it should or does it feel like something may be slipping, or does it feel normal as far as that goes but like the engine is bogging down?

Nope nothing like that or anything that would suggest a transmission issue/slipping. Engine doesn't bog down, no misfire, idles like nothing is wrong.

It's going but it just doesn't GO. It just feels like a little old lady is driving the car even if you floor it. :dunno:

 

[UnderFire]

Thought about spoiled gas as well but I never had any experience what spoiled gas does to a car. Will try the MAF, thanks!







Nope nothing like that or anything that would suggest a transmission issue/slipping. Engine doesn't bog down, no misfire, idles like nothing is wrong.



It's going but it just doesn't GO. It just feels like a little old lady is driving the car even if you floor it. :dunno:

Sounds fairly similar to my 4Runner when I first got it going after sitting for a year or so. It slowly got better over the first couple fill up and has been going strong ever since. Never replaced anything.

Sent from my JSN-L23 using Tapatalk

 

[triangles]

What HiLife said.

Remember these engines are drive by wire. If the gas is rotten and the knock sensor is detecting detonation the computer may be dialing things back and throttling things up slowly.

I'd top off with premium to make sure your octane is up and take it on the freeway for some high speed to blow all the cob webs out

 

[vincedprince]

Sounds fairly similar to my 4Runner when I first got it going after sitting for a year or so. It slowly got better over the first couple fill up and has been going strong ever since. Never replaced anything.

This is promising. As it sits, it has 3/4 on the gauge. I'm debating between siphoning the old gas out or just throw in a fuel system additive and topping it off with fresh gas.

After dealing with changing the fuel filter (under intake manifold!), I don't like to throw more parts at it. lol

 

[vincedprince]

What HiLife said.

Remember these engines are drive by wire. If the gas is rotten and the knock sensor is detecting detonation the computer may be dialing things back and throttling things up slowly.

I'd top off with premium to make sure your octane is up and take it on the freeway for some high speed to blow all the cob webs out

Thanks for the response. It has 3/4 on the gauge. Would you siphon some out or just top it off with premium and some fuel system cleaner?

 

[UnderFire]

This is promising. As it sits, it has 3/4 on the gauge. I'm debating between siphoning the old gas out or just throw in a fuel system additive and topping it off with fresh gas.



After dealing with changing the fuel filter (under intake manifold!), I don't like to throw more parts at it. lol

I put a big bottle of seafoam in with the first few fill ups, probably snake oil but I figured it couldn't hurt to potentially lube up the injectors, fuel pump diaphragm and FPR a little bit. Run it as low as possible and fill it all the way to the top to make the process quick and easy.

The fuel filter location on the RZ motors is a real headscratcher since it could've gone under the floorboard like the V6, but that was too easy I guess. Luckily it's about the only job that's that big of a pain. It could be worse, could've been a starter on a V6 auto.

Sent from my JSN-L23 using Tapatalk

 

[vincedprince]

Just want to post an update. Finally got some sun today after a couple of days of rain here in SoCal. Emptied a 16oz can of Seafoam in the tank, let it idle for a bit and took it for a drive. It was definitely the old fuel causing the slow acceleration. Got some power back and the 4runner can now go past 50mph even uphill. Will top off once it goes past 1/2 and add a bottle of Techron. Thanks to all your replies!