Unusual idle after cleaning MAF and throttle body

[ShooterMcGavin]

After I cleaned the MAF and throttle body, I had extremely high idle, like 1800+ rpms when warm. I disconnected the battery for several minutes to reset the ECU and then parked it overnight. Now, the idle is weird. For every car I have owned, the idle is usually high when it is cold. When I start the engine now, it struggles to get past 500 rpms and then goes up to 600 rpms. No higher. After it warms up, it settles at about 1100, which is still high. I've read and searched about high idle issues, so I know how to work with that (washer trick). Why is my engine now struggling, when starting, to just maintain 500+ rpms and then staying so low?

 

[WallyWest]

Just a wild guess, but you say you cleaned the MAF and throttle body. But not the IAC? So could some gunk possibly have gotten blown into the IAC and screwed it up?

Bottom line, if an engine is struggling to run it's not getting air, fuel, and/or spark, in the right quantity. Since you just messed around with the air intake side of things I would lean towards it's not getting enough air for some reason. Or too much air, as the case may be.

 

[ShooterMcGavin]

Good idea. I will be taking the truck off the road soon, to install some things and take engine things apart for maintenance. I'll check the IAC when I have things apart.

 

[A.Wilson013]

I'd put my money on a vacuum leak. Did you remove the TB to clean it?

 

[ShooterMcGavin]

I looked pretty thoroughly for a possible vacuum leak; couldn't find anything. I didn't remove the throttle body to clean it. I only removed the intake pipe.

 

[BrianSD_42]

There are several past threads where people have cleaned (I read scrubbed) the carbon off the inside of their TB and after installing it back on it idled very high.

They theorized that after cleaning the carbon off the TB didn't close completely and air leaked through.

I think it is probably that OR quite likely you didn't install & tighten the cables to the exact factory spec required making it idle correctly.

If you force-ably adjust the idle cables (or incorrectly reinstall them) then the computer will slowly adjust over several days but even then it will still be wrong.

Best to install it to FSM specs the first time.

 

[Lassitor]

There are several past threads where people have cleaned (I read scrubbed) the carbon off the inside of their TB and after installing it back on it idled very high.

They theorized that after cleaning the carbon off the TB didn't close completely and air leaked through.

I think it is probably that OR quite likely you didn't install & tighten the cables to the exact factory spec required making it idle correctly.

If you force-ably adjust the idle cables (or incorrectly reinstall them) then the computer will slowly adjust over several days but even then it will still be wrong.

Best to install it to FSM specs the first time.

Hey Brian, looking to clean my TB sometime soon, was going to follow this write-up form 4runners.org. He doesn't mention having to remove/disconnect cables to do so. Am I missing something? Pardon the noob question, just getting into the t4r maintenance.

 

[BrianSD_42]

Its not a requirement but some people have removed the entire thing thoroughly cleaned it and then upon reinstall had the high idle.

What I did was buy a complete TB (with IAC) from eBay off an used parts retailer (modern version of junk yard) for about $120.

The TB was off a Tacoma and had less than 90k miles.

Then I had the mechanic install it and tight the cables properly. He only charged me 1/2 hour labor.

So my truck is at 230k miles but my TB and IAC are only at 130k miles.

 

[Andy in Pa]

Typically, when cleaning a throttle body, MAF sensor, IAC or anything along these lines, you are cleaning out carbon deposits that over the years has BLOCKED air flow through these devices. As this air flow gets blocked, the ECU makes adjustments to the TB, IAC and MAF sensor to maintain the correct idle.

So when these things get cleaned it creates MORE air flow and now the idle is going to be high. As long as you are 100% satisfied that you didn't incur any vacuum leaks, then leave it alone and drive it for a few days like this. The ECU will re-learn where it needs to be to maintain the correct rpm, and find its happy place again.

 

[Lassitor]

Its not a requirement but some people have removed the entire thing thoroughly cleaned it and then upon reinstall had the high idle.

What I did was buy a complete TB (with IAC) from eBay off an used parts retailer (modern version of junk yard) for about $120.

The TB was off a Tacoma and had less than 90k miles.

Then I had the mechanic install it and tight the cables properly. He only charged me 1/2 hour labor.

So my truck is at 230k miles but my TB and IAC are only at 130k miles.

OK, thanks! I definitely like the idea of a new TB, but I'll have to settle for cleaning for now.

 

[BrianSD_42]

So when these things get cleaned it creates MORE air flow and now the idle is going to be high. As long as you are 100% satisfied that you didn't incur any vacuum leaks, then leave it alone and drive it for a few days like this. The ECU will re-learn where it needs to be to maintain the correct rpm, and find its happy place again.

Agreed!

 

[gamefreakgc]

Wait, the logic is a little flawed here. At idle, the air bypasses the "butterfly valve" through a hole on the bottom which is adjusted by the IAC. Cleaning the throttle plate has no affect at idle unless you had a warped or damaged butterfly valve or throttle body housing. Only when you depress the throttle does the butterfly valve open.

If you cleaned it using a liquid cleaner such as MAF cleaner, it's possible it washed sediment down into the IAC through the hole and gunked it up, not allowing enough air to flow through to keep a steady idle. Instead of a gunked up throttle, you now have a gunked up idle bypass via the IAC. For that reason, it's much better to clean the throttle body using just shop rags, I've done this every time on mine with no issues with the IAC.

 

[ShooterMcGavin]

There are several past threads where people have cleaned (I read scrubbed) the carbon off the inside of their TB and after installing it back on it idled very high.

They theorized that after cleaning the carbon off the TB didn't close completely and air leaked through.

I think it is probably that OR quite likely you didn't install & tighten the cables to the exact factory spec required making it idle correctly.

If you force-ably adjust the idle cables (or incorrectly reinstall them) then the computer will slowly adjust over several days but even then it will still be wrong.

Best to install it to FSM specs the first time.

This is all true, however, I posted up because my idle is not high. It is LOW. That is why this is weird. Usually, when starting an engine (cold), the idle will go up to 1,000-1,500 rpms at first. Mine used to do that. Now, after a cold start, it goes to 600 rpms.

 

[nevada]

After I cleaned the MAF and throttle body, I had extremely high idle, like 1800+ rpms when warm. I disconnected the battery for several minutes to reset the ECU and then parked it overnight. Now, the idle is weird. For every car I have owned, the idle is usually high when it is cold. When I start the engine now, it struggles to get past 500 rpms and then goes up to 600 rpms. No higher. After it warms up, it settles at about 1100, which is still high. I've read and searched about high idle issues, so I know how to work with that (washer trick). Why is my engine now struggling, when starting, to just maintain 500+ rpms and then staying so low?

Just a wild guess, but you say you cleaned the MAF and throttle body. But not the IAC? So could some gunk possibly have gotten blown into the IAC and screwed it up?

Bottom line, if an engine is struggling to run it's not getting air, fuel, and/or spark, in the right quantity. Since you just messed around with the air intake side of things I would lean towards it's not getting enough air for some reason. Or too much air, as the case may be.

I would guess this.

also, its typical after cleaning, or other adjustments being made, that it needs to relearn by being driven for a bit.

 

[Lassitor]

Wait, the logic is a little flawed here. At idle, the air bypasses the "butterfly valve" through a hole on the bottom which is adjusted by the IAC. Cleaning the throttle plate has no affect at idle unless you had a warped or damaged butterfly valve or throttle body housing. Only when you depress the throttle does the butterfly valve open.

If you cleaned it using a liquid cleaner such as MAF cleaner, it's possible it washed sediment down into the IAC through the hole and gunked it up, not allowing enough air to flow through to keep a steady idle. Instead of a gunked up throttle, you now have a gunked up idle bypass via the IAC. For that reason, it's much better to clean the throttle body using just shop rags, I've done this every time on mine with no issues with the IAC.

So, do you just use rags or do you spray the rag with some MAF cleaner, then clean?

 

[cek77]

I would follow the diy and remove it (lean it forward) so you can get behind it. Make sure the whole deal is clean. I just did my MAF and TB. Get a new gasket, put it back together. If you go that route might as well clean the IAC. I didn't because I was rushing to get it done for inspection and didn't have the IAC gasket to replace....but mine idles rock solid now so I'm not going to open it up.

 

[gamefreakgc]

So, do you just use rags or do you spray the rag with some MAF cleaner, then clean?

I usually just use rags. The deposits that accumulate come off pretty easy if you rub them off. I did soak the rags it once for a real bad job then clean it off but carb cleaner evaporates so fast that it doesn't last long.

 

[cccolin]

bumping an old thread, but I'm having this exact issue. I was getting erratic acceleration surging at hard throttle, so I got some MAF cleaner and carefully sprayed out my MAF sensor. While I was in there, I noticed the throttle body had a ton of buildup in it. So I cleaned it out with a rag and the MAF spray.

The first day or two after, acceleration and idle were all over the place. Eventually, the acceleration smoothed out, but the idle did not. I was hoping that the FI system would level itself out, but it hasn't. driving is totally fine, no issues at all. runs fine, accelerates fine, etc. But idle is really erratic and usually high. Most of the time, right after starting it, it will idle around 1800 for the first few minutes of driving. It usually, but not always, settles down to 1200 or so. Occasionally it will go down to around 900. If I rev it for a second at a stop, sometimes it settles down to a normal idle, sometimes it doesnt.

so what's the deal? did I fry my MAF, or maybe plug some passageways in the throttlebody while cleaning it that are messing with the vacuum?

 

[Kanoe]

If you sprayed anything in the TB while it was attached to the truck there is the distinct possibility you got crud down inside the IAC valve. That is a cleaning procedure that is best done off the truck(or very carefully).

One thread a few months ago regarding this issue the poster had gotten a little bit of plastic down in the IAC. Same result.

 

[gamefreakgc]

bumping an old thread, but I'm having this exact issue. I was getting erratic acceleration surging at hard throttle, so I got some MAF cleaner and carefully sprayed out my MAF sensor. While I was in there, I noticed the throttle body had a ton of buildup in it. So I cleaned it out with a rag and the MAF spray.

The first day or two after, acceleration and idle were all over the place. Eventually, the acceleration smoothed out, but the idle did not. I was hoping that the FI system would level itself out, but it hasn't. driving is totally fine, no issues at all. runs fine, accelerates fine, etc. But idle is really erratic and usually high. Most of the time, right after starting it, it will idle around 1800 for the first few minutes of driving. It usually, but not always, settles down to 1200 or so. Occasionally it will go down to around 900. If I rev it for a second at a stop, sometimes it settles down to a normal idle, sometimes it doesnt.

so what's the deal? did I fry my MAF, or maybe plug some passageways in the throttlebody while cleaning it that are messing with the vacuum?

Check to make sure the throttle plate is closing all the way as well. If it stays open even just a little it will greatly affect the idle.