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Discussion Starter #1
Well today I decided to clean the throttle bodies on my 96 with the 3.5L.

It all went smooth untill I went to start it. Once I started it it idled at 1400rpm!!

I had removed the throttle posistion sensor so I could clean the throttle, so I thought maybe I got something out of alinment. Well after removing the sensor from the throttle body and then starting the car, (to see if that would lower the idle)I got good old code 24.


So after I reset the PCM and then started the car all was good, back idleing at 700rpm. WTF... why would it do that?


One more question does all the carbon in the intake plenum comprimise performance?
 

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What probably happened is when you removed the TPS and reinstalled it, you gave the pcm the wrong "zero" signal. It probably read the TPS and thought you had the throttle depressed by the changed postion it was in. When you cleared the PCM by disconnecting the batery, the PCM read the intial TPS postion and set it as zero in it's mapping. Presto! Proper idle speed again.
of course, when you took the TPS out of the system the car was saying "hey, somethings not right here!" and set the code.
The system was just working as designed.

The carbon in the intake manifold affects idle quality mostly as opposed to performance. The throttle body butterfly does not actually close off completely at idle but is ever so slightly open to allow air to pass. The soot builds up and closes this clearance off, forcing the air bypass to try and make up the difference. Result: poor idle quality.

Cheers

BJ:anon:
 

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Yes, yes it does. Carbon builds up and causes restriction in air flow. 1 because it sloooowly decreases volume and can block off passeges, again very slowly, and secondly its not exactly smooth either.
 

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Discussion Starter #5
Great White said:
What probably happened is when you removed the TPS and reinstalled it, you gave the pcm the wrong "zero" signal. It probably read the TPS and thought you had the throttle depressed by the changed postion it was in. When you cleared the PCM by disconnecting the batery, the PCM read the intial TPS postion and set it as zero in it's mapping. Presto! Proper idle speed again.
of course, when you took the TPS out of the system the car was saying "hey, somethings not right here!" and set the code.
The system was just working as designed.

The carbon in the intake manifold affects idle quality mostly as opposed to performance. The throttle body butterfly does not actually close off completely at idle but is ever so slightly open to allow air to pass. The soot builds up and closes this clearance off, forcing the air bypass to try and make up the difference. Result: poor idle quality.

Cheers

BJ:anon:

Cool I am glad it worked like it was supposed to. I didn't think removig the TPS would have done that! Learn somethig new every day!

Thanks for replies!!
 

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IN the end just don't waiste your time cleaning the intake. It's not just from the soot etc, but the fact that the EGR tubes go right into the intake, it just builds up and not much you can do aside from blocking off the EGR tubes, but thats not a good idea eithe.
 
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I recently bought a 3.5L manifold off of a junkyard engine and I've had it soaking in solvent for about a week trying to loosen that crap inside. I'm going to grit blast it later today to see if I can knock some more out of there. I usually wouldn't be too concerned about it but I'm going to port it so having a clean manifold helps. If you have access to either of these it helps a bit! I'll be posting pics soon in my other thread.
 

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By any chance, did u remove the Idle Air control motor when you cleaned the throttle body? If so, that is what probably caused the initial high idle. When it is reinstalled the pcm has to reset it upon reinstallation. I haven't known of idle issues when removing/reinstalling the TPS, but I guess anything's possible.
 

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Discussion Starter #11
froggy81500 said:
By any chance, did u remove the Idle Air control motor when you cleaned the throttle body? If so, that is what probably caused the initial high idle. When it is reinstalled the pcm has to reset it upon reinstallation. I haven't known of idle issues when removing/reinstalling the TPS, but I guess anything's possible.

I took the IAC motor out previously to clean, and I had no consequences with the idle. It was just with the TPS. Great White hit the nail on the head.


Gr8crash.... I will not remove the the plenum, what you say makes total sense, I never thought of the EGR being a primary factor to the crap in the plenum.
 

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Lol i don't think most people do. I mean those EGR tubes and also the PCV system bing in a lot of oil and **** up there. The combination of those 2 realyl gunk **** up. Kinda pointless to waste time cleaning it ya know, when ni 5k its gonna be filthy again
 

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Dont screw w/ taking the plenum off unless you know the torque specs and have a torque wrench. I just take out the IAC and take off the intake pipe from the filter and shoot carb cleaner on the butterfly and the IAC hole. Replace the IAC, keep the filter pipe off. Start the engine and shoot more carb cleaner in the plenum, dont suck up any rags etc. The carb cleaner will dissolve the carbon and you should hear a noticeable difference at idle. Like more of an airy sound.

-GB49
 

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Anyone here had a chance to play with water injection? I hear if its placed before the TB it really does a good job on EGR cars from keeping the intake manifolds from being coated with carbon deposits.

I have never seen the pulled manifolds on a WI'd EGR engine so I am curious how well it would actually work at keeping that chunk off.
 

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gr8crash said:
Lol i don't think most people do. I mean those EGR tubes and also the PCV system bing in a lot of oil and **** up there. The combination of those 2 realyl gunk **** up. Kinda pointless to waste time cleaning it ya know, when ni 5k its gonna be filthy again
hey arron why take a shower if your just going to get dirty ? :moon2:
 

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shelbydodgeimp said:
Anyone here had a chance to play with water injection? I hear if its placed before the TB it really does a good job on EGR cars from keeping the intake manifolds from being coated with carbon deposits.

I have never seen the pulled manifolds on a WI'd EGR engine so I am curious how well it would actually work at keeping that chunk off.
Water injection used is to lower combustion temperatures and stave off detonation, don't know if it has any effect on manifold "hygene", but i have read a few articles that say there is some benefit in the carbon reduction department.
we used to run water/ alchol injection on high compression engines and blower motors for detonation resistance. Apparently, the tubo boys are using it now for the same reasons, from what I understand.

Cheers

BJ:anon:
 

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One of my instructors took a garden hose and with his engine running sprayed water down the carb, when it started to die he opened the throttle a bit, when it was running better he sprayed more water into it, and kept repeating until the car was at full throttle and the garden hose was full blast. He then shut the car down and tore the engine down for a rebuild and it was clean as a whistle. I know your not talking about that much water but if you want your engine clean this is most certainly one idea of many.
 

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Discussion Starter #18
Chewievette said:
One of my instructors took a garden hose and with his engine running sprayed water down the carb, when it started to die he opened the throttle a bit, when it was running better he sprayed more water into it, and kept repeating until the car was at full throttle and the garden hose was full blast. He then shut the car down and tore the engine down for a rebuild and it was clean as a whistle. I know your not talking about that much water but if you want your engine clean this is most certainly one idea of many.

Thats sounds scary to me, but I bet it does work well.
 

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shelbydodgeimp said:
ever seen an engine hydroloc?
Yup, it aint pretty! I'm not about to try it, but I thought that I'd relay the info.
 
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