Throttle Body - Engine Rpm

[Qwerty]

Hi all,

I have a corolla AE100 (yom: 1995) and it has the following problem. I need your kind advice on this issue.

When I tuned up the engine last time (an year back), I reported to the mechanic that the pulling power was not enough. He said it was because the engine rpm was low (around 400-500) and it should be around 700 for normal operation. Then he said after the tune up the rpm has come to the normal level. I too felt that the engine got more power after the tune up.

Then after around 2 months time, I could feel that the rpm has gone down as it was previously. According to one of my friends suggestion, I cleaned the throttle body myself. Then the rpm has come to the norml level.

But again the same happened after around 2 months time. This indicated me (don't know whether it is true) that there is some relationship between the TB and the rpm. while I cleaned the throttle body, I didn't see much corbon deposits also.

Is there any relationship between the throttle body deposit and rpm? That is like when the TB gets dirty, engine rpm goes down.

Is there any specific reason for the throttle body gettig more deposits in less time?

Please, I need your expert advice.

[Nilantha]

r u using LPG? What is the condition of air filter and petrol filter?

Edited August 6, 2007 by Nilantha

[Qwerty]

r u using LPG?

No. I use petrol (octane 90).

[The Don]

Hi,

Yes the throttle body controls the engine RPM, There is a sensor called the throttle sensor which detects the throttle position and increase the engine rpm accordingly as the accelerator paddle is pressed. The idle rpm is usually adjusted using a screw in the throttle body, which is how mechanics adjust the idle rpm. There is also another switch, or switch+sensor called a throttle controller (I appologise I am speaking with my knowledge of Mitsubishi engine, but I am told there is such a controller in all cars) which the ECU can use to adjust the idle rpm based on things such as idle engine load (to stop the car from stalling) and the air conditioner coming on,

I am surprised your idle RPM keeps dropping, which might indicate a problem with one of the above electronic components, then again it could be something simple, but to be on the safe side I suggest you go to the place you got the tune up done and report the problem, and if they struggle to explain it, to run an engine diagnostic,

Regards,

The Don

[Qwerty]

Hi,

Yes the throttle body controls the engine RPM, There is a sensor called the throttle sensor which detects the throttle position and increase the engine rpm accordingly as the accelerator paddle is pressed. The idle rpm is usually adjusted using a screw in the throttle body, which is how mechanics adjust the idle rpm. There is also another switch, or switch+sensor called a throttle controller (I appologise I am speaking with my knowledge of Mitsubishi engine, but I am told there is such a controller in all cars) which the ECU can use to adjust the idle rpm based on things such as idle engine load (to stop the car from stalling) and the air conditioner coming on,

I am surprised your idle RPM keeps dropping, which might indicate a problem with one of the above electronic components, then again it could be something simple, but to be on the safe side I suggest you go to the place you got the tune up done and report the problem, and if they struggle to explain it, to run an engine diagnostic,

Regards,

The Don

Thanks a lot for the reply.

But how the rpm become normal as soon as I clean the throttle body. What could cause the TB to get deposits more sooner.

Please advice.

[The Don]

Thanks a lot for the reply.

But how the rpm become normal as soon as I clean the throttle body. What could cause the TB to get deposits more sooner.

Please advice.

Well it could be that either something like residue or dirt is interfering with the operations of the throttle body. In the olden days if you had such a problem it was always some problem with the throttle body, but these days it tends to be electronics, I had a similar problem, and stupid M City recommended that I replace the throttle body, which I did at some expense only to find out that it was the electronics !!! and I couldn't return the throttle body back !!

Well if there are deposits accruing on the TB it could possibly be a bad air filter, could be both low quality or simply overwhelmed with dust, a leak in the air supply line from the air filter, If you had your throttle body professionally cleaned it should not be happening so soon after, I kind of suspect a lubrication issue with mechanical elements of your throttle body, or its simply worn, and at the point even the slightest amount of residue affects its performance,

as you can understand I am not a professional mechanic, and I haven't seen your car so the above are just guesses, its best if you run this issue through your own mechanic to see what he has to say, and as I say always get a second opinion if he declares it a major issue, because I found out the hard way !!

[gunat]

Not sure if it applies to your engine, but from a Toyota Perspective, there is also also what is called an Idle control, which can get sticky after extensive periods of use. When dirty, the idle can be lumpy/erratic. If your engine has one, see if cleaning that helps- but as suggested, go see a mechanic too.

[Qwerty]

Thanks all for the replies.

I'll go to my mechanic this weekend and see what he says.

I'll update the post with the info.

[maithri]

Hi,

Throttle body getting contaminated is a common occurence in many cars. Sometimes this can be alliviated by using a different brand/grade/or type of oil. First check if you have a engine breather attached to the air intake. If so clean it throughly and ensure any breather caps etc is working correctly-replace if faulty. Clean the throttle body with a good air intake cleaner-open the throttle and clean the edge of the butterfly-do not scrape as this will cause further prfoblems-soft cloth is best.

In my own car a Golf GTI I had this problem often and even being an experienced technician could not find a fault-I found the cure by accident when I used a different brand of oil at the next service-and never had the problem again-I still check the throttle body at every service and have little contamination or none at all-So try!

[Nilantha]

Yes, I also was thinking about this. I ask qwerty about air and oil filter conditions but he didn’t reply it. I think this can be minimized using Quality engine oil, genuine oil and Air filter

Remember Quality engine oil, genuine oil and Air filter are mostly important in good fuel economy, engine ware as well as for long lasting catelic converters and Oxygen censers.

[Arc Angel]

Yes, I also was thinking about this. I ask qwerty about air and oil filter conditions but he didn’t reply it. I think this can be minimized using Quality engine oil, genuine oil and Air filter

Remember Quality engine oil, genuine oil and Air filter are mostly important in good fuel economy, engine ware as well as for long lasting catelic converters and Oxygen censers.

machan why don't call Zakie (777508864). He's the man for any tune up.

[Ripper]

No to hijack the thread

I also have a little similar issue with ma sprinter... it idles at a little over 1000 but tends to go down to 700 or so and jump up back again to 1000+...

No major effect on performance except that it's a little irritating when the car does something it shouldn't be doing :)

I also though it was a dirty throttle body...

Maybe i should also get it checked out for "educational purposes" at least