Engine surging and inconsistent, sometimes high idle

I just purchased a 2002 4x4 Tacoma with the 2.7 3RZ-FE.

On the drive home, I discovered that when I put the car in neutral while coasting to a stop, the idle would drop to around 1,000, then rise to 1,700 or so, drop again, and repeat, until I came to a stop. At that point, the speed would start to climb, and top out around 2,000. One time, after 20 or 30 seconds, it started bobbing between 1 and 2,000, but at the rest of the stops, it maintained about 2,000 revs until I set off again.

I haven't had much time to look into possible causes, but I had a few minutes to look over the engine bay. My first inclination was that the MAF sensor might have something to do with it, since some change in engine behavior occurs when the truck comes to a stop, and perhaps the extra air pressure was messing with it. I unscrewed it, and it didn't look catastrophically dirty. Blowing on it with compressed air changed idle speed, so it's not completely nonfunctional, for whatever that's worth.

I also opened the oil cap, and discovered quite a lot of blow-by. My fingers are crossed that this just means the valves haven't been adjusted in some time. The engine has 270,000 miles on it, so I'd probably be more surprised if the valves are well adjusted than if they're way out of whack. I have a manual on the way, and will be adjusting the valves as soon as I can. I'm doubting this alone will solve the wandering in neutral issue, but maybe it will keep the idle lower...?

For a start, I'll be looking over the PCV and vacuum lines, as well as testing spark plugs and wires, though I'm doubting those are responsible.

Anyone have experience with these specific symptoms? Any ideas? Thanks in advance!

 

Don't think you can unscrew a MAF sensor. Not sure what you unscrewed. O2 sensor in exhaust manifold? Check engine light is off? Any pending fault codes? need more info.

 

I had the same problem. Cleaned maf sensor and then got a check engine light replaced air/fuel ratio sensor (o2) and mine has not done that since.

 

mechanicjon,

Whatever I unscrewed was just past the air filter, on the intake side, similar to what's shown in this picture:



I should have clarified, the CEL is not on, and the truck passed smog (I live in CA) two days ago. My understanding is smog techs check what the O2 sensors are reading, but maybe that depends on the day, the tech, and how sophisticated a vehicle's monitoring systems are...

Does the idle air control valve seem like a likely culprit? I've found a few descriptions of similar problems solved by replacing or cleaning it.

Thanks for the input!

 

MAF/air temp is on the air intake tube, two screws and it pulls right out

 

Gotcha. If it passed emissions there was no codes. It can't hurt to clean the throttle body and IAC really good.

 

I'm just guessing here. But what about a the crank or throttle sensor being dirty or out of spec ?
Or vacuum leaks.

 

So, the culprit did turn out to be the idle control valve. I'm not sure why, but the coolant was low, and it wasn't receiving enough to adjust properly. Did a pressure test, and didn't find any leaks in the coolant system. I'll carry some extra water around with me just in case...

It's not what I expected, but it's now idling at 700rpm. For the sake of anyone experiencing similar issues and searching for relevant info, I'll include the words solved and fixed. Check coolant!

 

Check into o2 sensors. Possibly look into cleaning your throttle body. Also the maf. If none of that look into a vacuum diagram and start tracing vacuum hoses. Pretty cool taco. Love 2jz's. Good luck man

 

Sorry disregard last post. Didn't read that you figures it out.

 

One problem solved, naturally another pops up...

After topping off coolant (engine was warm), idle was right where it should be, and I drove the truck for a while. Idle crept up slowly to 1,000, but I didn't think much of it, since that's much better than the 2,000 it was doing. I let the truck cool down for a bit, then changed spark plugs and vacuum lines. Started it up again, and it seemed a bit cranky, idled at 500-600 briefly. After maybe 20 seconds, idle went back towards 700, and I was happy. It didn't sound like it was missing, misfiring, not getting fuel to a cylinder, etc. Seemed plenty smooth, just low, as if running lean. Today, I went out again, and the engine fired up as usual, but it wouldn't hold idle. Less than a second after the starter motor stopped, it would die.

After 4 or 5 attempts, I gave it some gas, just enough to hold it at 1,000, and I'd slowly back off, until it felt like it was about to die, hold it for another second or two and repeat. It took less than a minute for it to hold at 600-700 by itself. I drove it a good 20 miles, and as the engine warmed, idle rose again, not quite to 1,000.

So... Ideas?

 

Do you have away to read live ECM data. OBD2 scanner?

 

Afraid not... Only other car is an '83 944, so I haven't had any use for one until now.

 

around $20 bucks on Amazon. well worth the money

 

I've used them before on other cars. Definitely on my to-buy list.

 

If you are looking a phone based app I'd recommend obd fusion. Use it with a wifi adapter on my iPhone. Helped me determin I had a bad air/fuel ratio sensor. App was $5 I think and the adapter was $10 I think. Works well. Can clear cel and codes.

 

I think this is the same thing my truck is doing. Same truck and motor, only 1999 model. It's at the 250k mark. When I bought the truck it had about 185k-ish on it. I bought it from a good family friend who threw in plugs and wires. It was throwing a code and he said that was what he was told would fix it. I've replaced the plugs, wires, and coil packs 3 times since. The first two times it ran fine for a while, then same thing. This last time nothing changed, I believe that's simply because it's gotten so bad. Keeps throwing a misfire code on cylinder 3. Truck idles rough and sounds pitiful. While driving the truck randomly surges and the entire truck kinda rattles. Of course as this is happening the CEL blinks also. I've found myself riding the clutch a bit, due to the lack of power, to keep it from stalling. In the event I do stall out, it is an absolute pain to crank again. Have to pet the gas like it's an old 2 stroke dirt bike or something. (Not sure if that's actually related, but I think so.) Got to talking with a friend who is a Toyota tech, and just telling him the symptoms, he thinks it's the head gasket. Claims these motors, while not notorious, are prone to have head gasket/head issues and when they are misfiring that's typically what it is. Luckily, I just picked up a motor today for it.

 

Should show up on compression test I would think. or water getting in cylinder

 

I suspect my issues are different... The truck still hasn't thrown any codes for me, and idle is quite smooth, just too low upon starting. Idle doesn't move around while driving for me after it's reached temperature. No lurching or anything... And mine does start right up. It feels very much like a fuel delivery issue, rather than compression related. The engine feels plenty powerful, too, so I'd be shocked if compression was lousy.

I'm thinking it's worth me double checking there aren't any vacuum leaks, and maybe seeing about thoroughly cleaning the idle control valve.

 

So, it's been a while... Here's the update.

The head was cracked in 2 cylinders, causing coolant level to drop, meaning the ICV couldn't do it's job. The code I got when I replaced the ICV was do to a wire coming loose that I didn't notice. 1 new head, reattached wire later, and 3k miles later, all is as it should be. Idle at 700 when warm, no more coolant consumption.