20v start engine idling style, dancing.

Acoustic

1,000 RPM
Senior Member
Nov 24, 2003
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Hi guys,

I noticed a few symptoms, but don't understand, please discuss.

There is only correct way that I am confident to say about, which is the moment engine start it will rev up to around 1500rpm then drop down to 900rpm, then steady all the way. Everything happens in 3 seconds or so.

Then I've experience many wrong & bad type of start procedures, as well as bad idling then appears good, finally affecting engine operations (fuel econ / performance)

My first runnable transplant was start engine, idling high 2000rpm, drive normally after one week will idle at 900rpm. Until remove battery from ecu, then repeat this so called ecu learning. Long time later then realized two vacuum hose installed wrong direction. I forgot which. So this is a bad idle that appears good. Fuel economy was good, engine performance was fine. Bonus finding, in order to make the ecu learn quickly, all I need to do is race the engine from first gear to third gear all 8k shift, one cycle enough.

The second type is worst & most harmful, because engine start 900rpm, without rev up then down. Just appear so good and constant and good boy. But I think one symptom very obvious, which is engine temperatures changes affects idling up or down. I think is hot up, cold down.

---------- Post added at 04:58 PM ---------- 6 hour anti-bump limit - Previous post was at 04:49 PM ----------

Second type is probably dead ISCV ???? dead water temp sensor?????

Third type is my current problem, engine start rev to 3000rpm then drop to 600rpm. This time I screw up the Idle Up Vacuum Pusher, TPS, etc.
 
Last edited:

me2kimi

500 RPM
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Jun 25, 2007
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Hi sifu,

From my experienced, I have tried to cleaned ISCV. A problem that I've found is there is a very small sand inside the rotary valve.
I need to take out the inlet & outlet pipe for the ISCV then clean it using brush. By manually turning rotary valve, I can feel roughness inside it.

IMHO, RPM speed is control by ecu (ISCV). Dashpot is use to to push TB a bit when there is no vacuum. So RPM should be higher when engine just start running. After enough vacuum created, dashpot will retract a bit.
 

Acoustic

1,000 RPM
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Thread starter
Nov 24, 2003
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Hi me2kini,

I read your other posts of cleaning ISCV, but this reminder of yours really makes me remember, especially the small little stone problem. I kept my faulty ISCV, will clean it next time as standby.

Thanks for explaining start engine no vacuum, then dashpot retract when vacuum level reached. Very good & important point.

Then I am stuck with above question/problem, please help give guidance: -
  1. my olden time, idling high, but reduce after 1 week time, or after 1 racing cycle, why what how ??? I'm confused, only know some vacuum hoses terbalik, but didn't dig to understand which is which.
  2. now, idling speed changes, unconfirm due to water temp or something else. cold start 500rpm engine dies. must throttle, force jalan, then OK after 100 meters. 750rpm. or less.
pengsang

Vacuum Lines for Toyota 4A-G 20v AFM 1993

there's a total of 5 links with multiple pictures, I better study them again. Can't believe I forgot all of them, throw back to teacher.
 

me2kimi

500 RPM
Senior Member
Jun 25, 2007
717
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Puchong
Your website help me alot when troubleshooting idle problem on svtop.
I have strange experience also, after send my car to car wash and clean engine as well, engine suddenly became better idle.
Smooth acceleration. I'm so happy that time.
But it only remain for about a week only.
Then idle rough again.

Sent from my Galaxy Nexus
 

^pomen_GTR^

7,000 RPM
Senior Member
May 13, 2010
7,509
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1,713
The Mines
Your website help me alot when troubleshooting idle problem on svtop.
I have strange experience also, after send my car to car wash and clean engine as well, engine suddenly became better idle.
Smooth acceleration. I'm so happy that time.
But it only remain for about a week only.
Then idle rough again.

Sent from my Galaxy Nexus
then u shud wash your car every week :p
 

Acoustic

1,000 RPM
Senior Member
Thread starter
Nov 24, 2003
1,295
52
3,148
Hong Kong
www.my-acoustic.com
Your website help me alot when troubleshooting idle problem on svtop.
oh yeah I remember now your blog describes with pictures a lot of ISCV cleaning, it was very good to read.

next time TTT come lah.
 

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