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Cold Engine Rpm Low After Throttle Body Cleaning

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Greetings to all fellow corolla owners here,

Before the throttle body cleaning, my 2001 Toyota Corolla LE with 94,500 miles used to start really easy in the morning. Upon starting the engine when it's cold, it would idle at ~1,500 rpm until the engine warms. When the engine is all warm up from driving it, the rpm would lower to ~ 650 rpm.

After the throttle body cleaning, the engine seems harder to start in the morning. And the biggest difference is that the rpm would be at ~900 rpm instead of the normal 1,500 rpm like it used to be.

I have since driven the car for over 50 miles on the freeway thinking that would clear out all the throttle body cleaner fluid/residue. The car drives and accelerates fine. It just that it doesn't start as easy in the morning and the rpm is too low for a cold engine.

Does anyone know what could be the problem? Could I spray too much throttle body cleaner fluid and that could foul up the sparks plug, IAC or something else?

Thanks for all the help!


I forgot to mention that the MAP sensor was cleaned a week ago with great result. The car ran a little smoother and has a little more pep after the MAF sensor cleaning.

It is only after I cleaned the throttle body that the engine has low rpm upon start up when it's cold. This behavior is definitely caused by the throttle body cleaning.

I removed the double post - so that you get more attention to your topic / don't get the replies split between them.

Couple of questions to get some more info:

Did you make sure you cleaned both the MAF sensor wires inside a tube and an exposed IAT sensor on the side? Usually in the process of hosing down the sensor with solvent, you'll get both in the process.

How did you clean the throttle body - was it still attached to the car or did you remove it?

As for idle speeds at cold start - between 850 and 1500 rpms is what I get, depending on ambient temps. Idle should drop in the 650-750 rpm range when warmed up. So what you are seeing sounds about right to me. If the car "shakes" on a cold start - could be a sign of a vacuum leak.

Note that it could take a little while for the car to "relearn" air fuel maps, depends on where it was before you started. You could speed it up slightly by resetting the ECM after the cleaning - start from a clean slate.

Definitely double check the plugs - make sure they are not fouled. Also double check the vacuum lines - since you had to pull some of induction system away from the throttle body to get at it - possible a vacuum line fell off, or was damaged in the process. Just do a visual check and make sure all vacuum ports had something attached to them (line or plug) - note if any there are any rubber hoses just laying around.


Thanks for the reply fish! After driving the car for 2 weeks now, the low rpm issue when starting the engine cold has recently gone away. For the past 2 days now, the car started up easily and normally like it did all these years in the morning at ~1600 rpm instead at ~900 rpm. I believe the ECM finally adjusted itself?

But let me give you a little more detail as to why I clean the MAF sensor and the throttle body in the first place...

The car is a 2001 Toyota Corolla LE automatic with 94,5XX miles. The car was purchased new and it has been super dependable. In the 16 years that I own it, I never had to do any repair, just basic maintenance item (fluid change, brake pad, new tires, etc.). But lately, the engine has developed a mild vibrating/shaking issue when you stop at a red light or a stop sign. The vibration from the engine would cause the radiator to vibrate and rattle against the frame. Upon inspection, I discovered the two radiator upper bracket is shot. The rubber is all dry and crack. It no longer hold the radiator in place securely. I replaced the two old one with two new one (part #165330D010). With the two new upper bracket installed, the radiator rattling noise cause by the engine vibration has decrease a lot but it is still there.

In an attempt to solve the vibration problem, I did some googling and watched a youtube video by chasiu75 on how to clean the MAF sensor. Since the MAF sensor on my car was never clean before, the amber color part of the sensor was dirty. I cleaned it with CRC MAF Sensor cleaner. After the MAF cleaning, the car seems to run a little smoother and the vibration seems to be reduce by a little at idle.

Wanting more, the next thing I did was to clean the throttle body since it was never clean before. I use CRC throttle body cleaner along with a rag and a toothbrush to clean it. Again, I watched a youtube video on how to clean it. After the cleaning, the car won't start (spray too much and flooded the cylinder). I had to put the gas pedal to the floor and crank it a few time to finally start the car. The engine was running rough for a few minutes before finally smoothing itself out. I added a bottle of Chevron Techron Fuel Treatment, filled up the tank with gas and went out for a 30 min drive thinking that would let the ECM adjust itself. The next morning when I start the car is when I notice the engine rpm is way lower than it used to be when the engine is cold hence the original topic that I made here on this forum.

Fast forward to today, the low rpm issue when starting the engine cold in the morning has gone away but the engine vibration at idle has not. The engine idle vibration has become somewhat sporadic in nature now. Sometimes it would be smooth stop at a red light and sometimes it would vibrate causing the radiator to rattle.

The next thing I am planning to do is to change the valve cover gasket (#112130D040) and seal (#9021006013), pcv valve (#1220422051), and the spark plugs (SK16R11) since they all have never been change before. The parts should be arriving sometime next week.

Nice! Sounds like you are on the right track for the maintenance for this car. You are definitely hitting all the right parts for this age and mileage. Just stay onto of fluid and filter changes, addressing any dry rot issues (double check your vacuum hoses, the PCV hose when you replace the PCV valve) - and should get plenty of life out of the car.


The amber 'bulb' isn't the airflow sensor, the airflow sensor are the two wires at the base of the inside of the plastic stalk. If you're at almost 100,000 miles and you've never changed the spark plugs now would be a good time to do it when you do the valve cover gasket. I suggest Denso Iridium TT spark plugs, they'll easily last another 100,000 miles (or more). The 98-03 1ZZ engine (your engine) is known for consuming oil and having low compression as they age, it wouldn't be a bad idea to do a piston soak when the spark plugs are out, there's a lot of how-to's on that around the internet. I've heard great things about AC Delco X-66P upper end engine cleaner lately, it would be worth a shot. Between a clean MAF, clean upper end, and new plugs it should idle pretty nicely. The last step may be a new passenger side engine mount. Only use a dealer part for that, aftermarket ones are made of the wrong rubber and shake worse or last only a year or two.


Yes, when I cleaned the MAF sensor, I spray the amber color wire along with the two tiny wire inside the black plastic housing. I forgot to mention this in my reply. When reinstalling the map sensor, I made sure that it was properly inserted and the rubber gasket was properly seal to not let in any air.

All the hoses checked out fine. I don't see any cracked or anything.

For the spark plugs, I bought the genuine toyota plugs which is the Denso Long Life Iridium plugs (SK16R11). Is the Denso Iridium TT spark plugs mention by Bitter better?

I will look into the piston soak mention by Bitter. He also suggest replacing the passenger side engine mount. I notice the rattling noise/vibration "seems" to be coming from the passenger side so maybe that mount went bad. Is the correct toyota part number for that mount #12305-0D010?

Either plug will be fine. If you want the the longer lifespan, I'd stick with the OEM SK16R11, rated for about 120K miles. The Iridium TT are a thin wire twin-tip (they tipped the ground electrode with a platinum button) that supposed to last 100K miles. I've used both of them as well as NGK Iridium IX plugs - all work well on this engine.

As for the mount - that looks like the right part number. Before you jump to changing the isolator - try this quick test. While the engine is running and you notice the rattling/vibration - slide a floor jack under the oil pan with something soft over the jack pad and slightly jack up the engine. Not trying to lift up the car - just trying to unload that motor mount. If the vibration/rattling disappears - then you know that the mount is likely faulty.

If the noise doesn't change - I'd suspect something on the accessories - bad serpentine belt, bad belt tensioner, bad idler wheel, faulty pulley (bad bearing), etc. A quick test to isolate those is to run the engine without the serpentine belt on - this is OK as long as you don't run the engine too long. It will be quite evident if an accessory is bad once the engine runs without the serpentine belt - as the noise will completely disappear. If this is the case, then you'll just have to rotate the pulleys by hand (engine off) as see which one is loose / making noises.


I have driven the car for a week now since I replaced the valve cover gasket, pcv valve and the spark plugs. I can confidently say the problem is now fixed!!! There is no longer any excessive vibration coming from the engine when stopped at a red light or a stop sign. The car now idle smoothly like it was when it was brand new. The engine seems like it can run for another 100k miles. default_smile

I would like to mention the pcv valve (Toyota #12204-22051) and valve cover seal (Toyota #90210-06013) that I ordered are NOT compatible even though the parts system say it is. The correct pcv valve number is Toyota #12204-22041. I had to reorder this again. I reused the old valve cover seal since it seems to be in good shape.

All in all, I say this DIY is well worth it. Thanks so much for the help!


PCV Valve # 12204-22041 with green Loctite has M16 (16mm diameter) x 1.5mm threads.

It takes a 22mm or 7/8" (22.225mm) wrench or deep socket.

PCV Valve # 12204-22051 with pink Loctite has 3/8" BSP threads (16.6624mm diameter), 19 TPI (1.337mm threads).

It takes a 3/4" (19.05mm) or 19mm wrench or deep socket.

Valve cover gasket # 11213-0D040,,11213

Part # 90210-06013 is a seal washer (grommet) for one of two valve cover bolts.