Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Fast - Slow cycling at Idle


paulrs's Avatar
Visiting Guest

Posts: n/a

08-12-02, 04:13 PM   #1  
paulrs
Fast - Slow cycling at Idle

I have a 1990 GeoPrism (Toyota Corola) 4A-FE 4 cylinder engine.

At idle the engine drops down until near stall and then "catches" itself and speeds up. The cycle is then repeated as it drops down in speed to another near stall. The engine cycles this way both engaged and un-engaged. It does it when warm.

Any help appreciated.

Paul

 
Sponsored Links
bejay's Avatar
Member

Join Date: Dec 2001
Posts: 2,538

08-12-02, 04:43 PM   #2  
has any adjustments been made to the idle sometimes if the idle is set up above 1000 rpm the computer will cause a constant idle surge .

 
knuckles's Avatar
Visiting Guest

Posts: n/a

08-12-02, 11:15 PM   #3  
knuckles
Clean the throttle plates and idle air control valve.

 
paulrs's Avatar
Visiting Guest

Posts: n/a

08-13-02, 07:21 AM   #4  
paulrs
To Knuckles:

I have both Chiltons Big book and the specific Chilton Toyota (Prism) repair manual and the diagrams are not specific enough with names to identify the idle air control valve (The books use letters VSV, DP, etc. without identification). Could you point me in the right direction. I assume the throttle plates are inside the throttle at the mechanical pivot. Is that valve located at the end of the throttle with vacuum hose control? There is what appears to be an air temp sensor before the throttle in the intake area.

I have worked primarily on carbureated engines and have to learn the placement of fuel injected components. Thanks.

Paul

 
Joe_F's Avatar
Visiting Guest

Posts: n/a

08-13-02, 08:11 AM   #5  
Joe_F
Have a look at autolibrary as I have it bookmarked below.

 
paulrs's Avatar
Visiting Guest

Posts: n/a

08-13-02, 10:02 AM   #6  
paulrs
I discovered that the valve at the end of the manifold (opposite the air intake end) is called the ISC or Idle Speed Control valve.

Is this the one that should be cleaned?

Paul

 
Joe_F's Avatar
Visiting Guest

Posts: n/a

08-13-02, 10:12 AM   #7  
Joe_F
Once again, what does Autolibrary below have to say about it?

 
paulrs's Avatar
Visiting Guest

Posts: n/a

08-13-02, 10:30 AM   #8  
paulrs
(1) The autolibrary does not any info on 1990 Geo; 1990 Prism

(2) When I enter 1990 Corolla I do get to some info.

(3) The diagrams in intake manifold and throttle body do not match what I have.

(4) They do not index the idle air control valve NOR the idle speed control (component). The only way I learned what ISC was is in the general info on the fuel injected system.

(5) It would be nice to have a diagram that names all the various components for us newbies working on the higher tech engines.

This is a 90 Geo Prism 1.6L engine 4A-FE (VIN-6)

 
knuckles's Avatar
Visiting Guest

Posts: n/a

08-13-02, 10:16 PM   #9  
knuckles
Try 1990 Prizm. Note the spelling.

 
paulrs's Avatar
Visiting Guest

Posts: n/a

08-14-02, 06:26 PM   #10  
paulrs
OOPS! - on the spelling "PRIZM"

Got the needed information and will pull together the needed replacement gaskets and attempt to clean the throttle plates and air control valve.

I will report back next week if this "fix" worked. Thank you for all the help!

Paul

 
paulrs's Avatar
Visiting Guest

Posts: n/a

08-20-02, 03:24 PM   #11  
paulrs
Cleaning the Idle Air Valve solved the problem!
A special thanks to "Knuckles."
When I disassembled the Prizm's Throttle Body, the dirt had settled at the output of the Idle Air Valve around the Needle Valve adjuster. I seated the needle valve, counting the turns 1-1/4 and then removed it to clean things out. Initially I used gasoline rags and cotton swabs. I then poured in some carb cleaner to get out any other accumulation. I put back the needle valve, seating it and backing it out the 1-1/4 turns and put everything back together. It is now running a smooth idle. Thanks again to all who helped.

Paul

 
Search this Thread