Shake! Shake! Shake! Shake!...at idle.

[Jennfong Wu]

Need some ideas about the following symptoms for my 97 DE:

1. The engine shakes when idling. But it does not shake as much when RPM is higher than 1300.
2. The check engine light once came up for P0301 (Cylinder #1 misfired).
3. I went ahead to clean the throttle body with the passive holes pluged (as instructed by service manual). After that, I feel the acceleration is easier. But the idle sometimes will hold at 1200 RPM. In order to get it down to 750 RPM, I have to slightly race the engine to get it down. Or if it dose not come down after racing the engine, I have to keep the A/C ON in order to keep it at 750 RPM.
4. And then the 2nd check engine light came up for P0505 (Idle control system malfunction). While the car is still shaking at idle.

Question:
a. Is my IAC gone bad? For the symptoms I observed, it seems to me that it was dying because I possibly let the cleaner enter the passive holes during the throttle body cleaning. But why it can still hold the idle perfectly at 750 RPM when A/C is ON?

b. Has anyone been ever disassembled/cleaned/repaired the 7G IAC?

c. No clue about the P0301. I replaced the spark plugs, wires, cap, and rotor. A local garage tried to find the cause but everything seems to be allright (fuel pump, injector, ...). The only word that I got from the local garage is that the #1 plug tip is a little bit white (meaning is hungery for fuel).

Any suggestion will be appreciated.

Jennfong

[Proto]

Sounds to me as the IAC went bad causing it to idle high. With the AC on it puts more load on the engine at idle causing the lower idle.

[frag_daddy_2007]

i have had the IAC code come on before and i will tell you, the plug on the back of the throttle body has a habit of coming loose which will cause an idle issue and that code

look on the back of the tb and push that plug back in if it is loose, worth a shot...

[Jennfong Wu]

I'll give it a shot to disconnect/re-connect that plug and see if the CEL will come up again.
On the other hand, I am wondering if I can clean the IAC myself by disassemble the black piece where the harness plugs in (as shown in the IAC photo from the following link)? Anybody has disassembled this IAC before?

http://www.autozone.com/N,314589/initialAction,partTypeResultSet/initialN,15900207/shopping/vehicleSelect4.htm

Jennfong

[Jennfong Wu]

Problem is finally solved! It was the intake leak around cylinder #1 (P0301) and faulty idle air control motor (P0505).

Week ago I finally made up my mind to spend the bucks and have the Idle Air Control Motor ($250 part) replaced by the local garage since there was no doubt due to the code P0505. After he finished up the replacement and was verifying everyting is in place as they should be, he noticed some minor Sssssss sound at the intake manifold. He went ahead to replace the gasket between the intake manifold and cylinder head. Then the erased trouble codes never come up and it has been a week or so.

Lessons learned (apparently the hard way):
1. The the P030X code comes up several times and is dedicating itself to a specific cylinder, then the problem should be just limited to that specific cylinder. It could be the intake leak, exhaust leak, faulty spark plug, faulty plug wire, or worn valve. Focus on the things that are only for that specific cylinder, not the things that involve with the rest of working cylinders (such as IAC, throttle body).
2. I took the wrong guess and thought there might be something wrong with the throttle body. So when there was only P0301 at the very begining, I didn't follow the correct steps to clean the throttle body which kills the IAC because the solvent entered the IAC through the passage holes.
3. Simple problem was fixed at high price: As far as I can recall, here is a list of stuff I replaced since the guy in Autozone found me this P0301. a. Spark Plug Wire Set, b. Distributor Cap, c. Distributor Rotor, d. front Oxygen Senor, e. rear Oxygen Sensor, f. PCV Valve, g. Cleaning Throttle Body (just servicing, no replacement), h. IAC Motor, i. intake manifold gasket.--------only item "i" truely resolves the issue. But the good thing that comes after all these replacements is now my gas mileage jump from 23mpg to 25mpg (city). Hopfully the better gas mileage will leverage some saving from these expenses.

Thank everybody for the info.

Jennfong

[bronxbombr]

Problem is finally solved! It was the intake leak around cylinder #1 (P0301) and faulty idle air control motor (P0505).

Week ago I finally made up my mind to spend the bucks and have the Idle Air Control Motor ($250 part) replaced by the local garage since there was no doubt due to the code P0505.
Jennfong

Now i know i be selling my stuff too cheap. Have 2 brand new ones left.

[bmxmike]

That sounds about right. Autozone wants over $150 i think. I just go to a junkyard and grab them for like $10. I took the IAC apart one time and its not that difficult. I was trying to test it to see if it wasnt working but all the diagrams i had where for different cars. Cause it tell you to hook up a mulitmeter to the iac and check the resitance between pins. Just if you even do be carefull with the sping and wheel! Almost lost them cause they flew out at me