RPM problem

Tiny
KAIKIING
  • MEMBER
  • 1994 TOYOTA COROLLA
  • 173,657 MILES
My car idle when start up and also during normal temperature in P rpm around 850 - 1000. After gear in R or D position, rpm drop until 550-750rpm. May I know what might the problem is?I've try to clean the throttle body and also check the vacuum leak. The engine can start up easily in cool condition but hard to start up in hot condition. Please advice. Thanks
Monday, October 3rd, 2011 AT 11:29 AM

14 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
I would be checking the idle control valve, also scan for any unresolved fault codes, start here.
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 11:52 AM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
I've check the IAC valve when I clean up the throttle body and it show function normally.I do the jumper check with at diagnostic port and the engine light show up 32 fault code which might be the MAP sensor.I try to switch with another car MAP sensor but look like nothing change. Any idea?Thanks
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 11:58 AM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Could be a coolant temp sensor out of range, this will git the starting problems you mentioned. Being out of range will not set a code, just screw up the hot & cold mixture settings.
Was this
answer
helpful?
Yes
No
+1
Monday, October 3rd, 2011 AT 12:02 PM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Any procedure or guide for that?
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:04 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
No, it's just a screw in sensor, you can test them, by checking the resistance against temp. There will be a graph to check against, I do not have it, it will be something you can get from a dealer.
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:16 PM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Is that mean it is adjustable?
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:23 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
No adjustable manually, it is in the coolant, with cold coolant the resistance of the sensor is such it sends a signal to the ECU to go rich, as the coolant heats up the resistance through the sensor changes and this sends the base mixture lean for normal running, in conjunction with other sensors that is, but the coolant temp sensor is the main sensor for cold start and base lean mixtures.
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:28 PM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Will that also causing rpm drop till******** when driving or reverse with break?
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:38 PM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Will that also causing rpm drop till not idle when driving or reverse with break?
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:47 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Not normally, this is more for the hot /cold stat problem, I feel that you need to get this sorted first and move on to the next problem, there may be some input from this sensor that can affect the other problem, but primary the starting problem.
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 12:57 PM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Yes.I also feel this is the primary problem.I've looking to solve this problem for quite long time already. Hopefully CTS will be the reason for it. But it is quite hard for me to get such spare for the car in my area.
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 1:27 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Where are you?
Was this
answer
helpful?
Yes
No
Monday, October 3rd, 2011 AT 9:56 PM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Malaysia area. Any suggestion for online purchasing?Thanks
Was this
answer
helpful?
Yes
No
Tuesday, October 4th, 2011 AT 3:38 AM
Tiny
KAIKIING
  • MEMBER
  • 44 POSTS
Hi,

I've change the CTS but still having hard start up problem during hot condition. But the car is much more idle after change. Is it normal there is only a little water coming out from the place of CTS after I unscrew it out?Any idea?Thanks
Was this
answer
helpful?
Yes
No
Wednesday, October 5th, 2011 AT 12:10 PM

Please login or register to post a reply.

Related Engine Low Power Content

Fix an Engine with Low Power!
VIDEO
Fix an Engine with Low Power!
Instructional repair video
Symptoms of Low Engine Power
GUIDE
Symptoms of Low Engine Power
The power your car's engine is producing is important. When you step on the gas you need your car to accelerate, mainly to keep you out of trouble when getting onto the...
VIEW MORE