When first started the RPM should go up to about 1,500, then if engine is cold it should drop to 1,000-1,200 depending on outside temp.
Then as engine warms up idle should drop to 700-750 for manual trans, 750-800 for automatic.
Warm engine should start with same 1,500 rpms then drop to "normal" within a few seconds, 10 max
RPMs staying up on a manual trans when shifting is normal, it is part of the computer software, I think its about 5 seconds, if you leave the clutch in it should start dropping after that.
1,100 rpms is kind of a magic number on most computers, when you are driving and take your foot off the gas(TPS = <1volt), the computer shuts off the injectors, this saves fuel while coasting, then at 1,100 rpms the computer turns the injectors back on at idle level, so a 1 or 2 second "hold' at 1,100 could be normal.
On models with electronic speedometer Computer will also hold idle at 1,000 until speed drops below 5mph
Regular startup routine for a fuel injected engine is pretty much the same for all of them.
Key on , EEC relay closes and starts computer, and fuel injectors get power as does coil.
Computer controls fuel injectors and coils by Grounding, so they are "off" but have 12 volts.
Computer turns on fuel pump for 2 seconds to prime fuel system
Computer opens IAC(idle air control) valve all the way, this is why the high idle at startup.
Computer checks ECT sensor for engine temperature.
Computer checks TPS(throttle position sensor) for 4.8volts, Wide Open Throttle(WOT), this would tell computer to shut off injectors while engine cranks, this is to clear a flooded engine, if TPS is 1volt or under "no foot on the gas pedal" it means start normally.
Computer ignores most other sensors at startup, O2 sensors are ignored for 5 to 10 minutes on cold engine and for 2 to 3 minutes when engine was already warm.
And just FYI, never replace sensors until you have tested them, most are simple to test with volt or OHM meter.
And OBD codes usually means sensors are working and the info they are sending to the computer shows a problem.
Things to try
After engine is warmed up let it idle and unplug the IAC valve, idle should drop down to 500-600, this idle is set by a screw on the throttle linkage, this is not for engine idle, the IAC controls that, this is for minimum idle in case the IAC fails.
Some people crank these in too much so computer can't drop idle below where screw is set.
Shut warm engine off, open throttle manually and remove cables, restart engine, see if idle has dropped down, if so then cable was too tight.
Also with engine running open throttle quickly and let it close, you are testing to make sure return spring is working well and there is no binding, which would cause RPM not to drop while driving.
Do the same test after hooking throttle cable back up, have someone push down the gas pedal and release it quickly, maybe cable needs to be lubed, it could be causing slow return.
I am an old carb and distributor guy too, and after learning a bit I think the new systems with sensors are way better, more complicated for sure, but much more reliable and less maintenance required.
Points, rotor and cap, carb leaks and tuning, it was simpler but there was always something wrong, lol, not undrivable but just a little tweak was needed.
What does the dash board temp gauge read?
Should be just below 1/2, if it is lower after warm up then thermostat could be stuck open, this causes engine to run too cool and fools the computer into thinking engine is not warmed up all the way so idle stays a bit high.
For these new systems t-stat is usually a 190+deg, operating temp needs to be 200-230deg for best MPG and lubrication, never use a 180deg unless t-stat is on lower rad hose, yes some put it there, lol.
Last edited by RonD; 01-13-2014 at 08:30 AM.