My 2003 MDX revs up and down while in Park and Neutral. It idles aggressively in Drive and Reverse, so much so that the dash will vibrate and I have to keep extra pressure on the break to keep the car still. There's also engine knock while idling in Drive and Reverse, but not in Park (it just revs up and down).

My mechanic said the revving is the TB. He reset it, but it went out a week later, that's when the engine knock started, out of the blue. I replaced the TB with a used one to save $ (donor car had 40K miles). I also replaced the timing belt and filled with premium gas. Engine knock and revving problem remained, and a couple days later blew a hose which caused the rpms to jump all over the place. Fixed the hose, replaced pvc valve and purge control valve solenoid, but knocking, revving and aggressive idle still exist. My mechanic's exhausted all options, and thinks the used TB might not be reprogramming properly.

Before I drop a bunch of $ on a new TB, does anyone know if you can install a used TB, and if so, do you need to do anything special to make sure it reprograms properly?

 

are you talking about a used timing belt???? you know they are only a few $$$.
Or, are you talking about throttle body?

It sounds like a sensor to me.

 

I would write down your radio code and navi code, if applicable, and then reset and disconnect the battery for about 30 minutes. That will clear all codes. See if the problem persists.

 

by TB you mean timing belt right?

Timing belts brand new are less than $50...get a new one. How many miles are on the MDX? You said you replaced the timing belt already, I don't know why it would continue to misfire unless the mechanic set the timing way off.


What did he reset? What went out a week later?


This will probably be moved to the MDX section soon..

 

There is no programming for a throttle body.

The problem is that the idle air control valve on the bottom of the throttle body is dirty. They can be removed (2 screws) and then cleaned with throttle body cleaner.

Is the check engine light on? Did it throw any codes?

Personally I would take it to the dealer. Engine knock is not something you just ignore. It can ultimately lead to catastrophic engine failure.

 

Thanks for the feedback and sorry about the confusion. The TB stands for "Throttle Body", not the timing belt. I installed a used throttle body and a new timing belt.

My mechanic reset the throttle body and it went out a week later. That's when the engine knock started.

The engine light isn't on and I don't know if it threw any codes.

I'll ask my mechanic if he cleaned it or try disconnecting the battery for 30 minutes. A trip to the dealer isn't out of the question either, but I've already spent so much $, I hate to spend a bunch more without some confidence the problems been isolated.

 

Thats odd that a code hasnt been thrown yet. I agree with NSXNEXT about looking into the idle air control valve.

 

Hmm.. Definitely pull any DTC's it threw. New TB and I'm guessing new MAP, MAF and Idle Air Control Valve? If not, check those then check the egr valve and clean it out.. If all those check out which I'm guessing one is at fault, then I suggest go down the line from easy fix to PITA and cross them off your list.

Check for vacuum leaks, soapy water or a long hose (not graphite) does wonders. If nothing then remove the intake manifold and check the gaskets for cracks. Then remove the plugs, check for fouling, and do a compression check and leak down test.

Also.. just to clear up all the details.. I assume you run 91+ octane religiously? Very interested in hearing more details and figuring out your issue. I'd be very surprised if you didn't blow your top ringland or cause some noticeable damage to your piston, get it scoped if you can while the plugs are out.