1996 Saturn SL2 244,000 DOHC. Thanks for your time. I have read through many posts on this forum looking for an answer but was not able to find anything duplicating my exact concern with the above vehicle. When I start my Saturn the rpm climbs to almost 3000 for a few seconds and then starts to fall ending up at what sounds and appears normal to me, at 900. No problems when on the road. Can come to stops without the RPM climbing, put it in neutral, park, whatever, no problems. Only when I start it does this occur. I can do it several times in a row and experience the RPM hike, which then returns to normal. I have cleaned the throttle body assembly. Lot's of carbon there. PCV is working, hose is in good shape. Removed the egr (replaced a year ago) and cleaned that also. Presently, I do not have a check engine light on. It is my understanding from reading past threads that my concerns may be the throttle Position Sensor (cleaned at point of connection to throttle assembly), Idle Air Control Sensor, possibly the Coolant temp sensor or maybe even the fuel filter/line, although I replaced that a couple of years ago. In order to avoid the best I can, a costly process of elimination repair what would most likely be the culprit in this scenario? Thanks for your time again. Pete

 

On a cold start there is the fuel injection equivelent of a carburators choke. The car will run rich untill it warms up increasing the idle speed. I would have to look up the circuit on how or why it works. If some one does not answer this better some time today I will look it up.
It sounds like this is sort of working as idle speed increases and then returns to normal.
The amount of increase depends on outside temperature and the temperature of the engine. 900 rpm idle is more or less normal. 700 rpm would be more normal, and accuracy of the tachometer is an open question.

 

Thanks for your time. I think it would be safe to say she is idleing at about 800 when she comes down. I should have said she idles high for about 5 seconds and takes another 5 to 10 to come down to that 800. It is definately not normal from past experience. Prior to cleaning the throttle assembly and egr it would only go to about 2500 then come down. I could tell then that something wasn't right. After cleaning both items is when I grew a bit more interested as it was getting closer to 3000. This all started during/after I was experiencing multiple miss fires, starting about a month ago. Replaced wires and plugs, still had a slight misfire only. Decided to clean up coil and ground then reconnected a couple wires wrong prior to start up. Flooded the heck out of motor and eventually got it started. No missing at this time, and no codes still, but still have the high idle at start up. I don't know if the missing is relative to my high idle concern, but I want to tackle this issue first. Thanks again for your time.

 

Okay, here's some new info. Went out and started the vehicle. Fuel pump kicked on for normal time, maybe close to 3 seconds. Started and shot to 2750 and then came down to 1000 and that sounded like a good idle. Turned off the engine. Turned key on, fuel pump short cycled, maybe one second, started the engine and no high rpm this time, maybe 1200. Was thinking maybe she fixed herself or recomputed something. Did it a couple more times, fuel pump short cycled and it started at a lower rpm. Decided to restart it one more time. Fuel pump cycled at what I believe was a normal cycle and it jumped right back up to a high idle to about the same as noted above, then came back down to maybe 1000.

 

This information while interesting as something to look at, is still indicitive as to how the Cold Start is supposed to work depending on outside temperature and temperature of the engine.
It also may be in part, a further symptom of the problem. Engine speed is determined (in part anyway) as to how much fuel the thing gets. This is in part determined by the size of the fuel injectors, how long they are turned on for and how much fuel pressure is being supplied to them.
Cold start is usually supported by an additional fuel injector located some where central to the intake manifold (on some engines) so the fuel from it can mix with the normal fuel source to insure the engine stays running when cold.
The question becomes in part, what controls cold start, how does it control it and if required what are other parameters involved. Such as what is fuel pressure. A number controlled by the fuel pump and a pressrue regulator on the fuel rail that supplies fuel to the injectors.
My answer is! I dunno! Untill I look up the service literature. There are variables involved that as a shade tree mechanic I do not see on a regular basis, but still know they are there to be found and determined.
Which requires looking things up in some form of a service document.
These range from simplistic yet usefull paperpack books from your auto parts store to a full blown factory service manual.
After 16 years, I have not had to investigate how my Saturn fuel injection works. It works just fine.
I have owned a number of fuel injected high mileage cars where the fuel pump quits. That is fun to determine.
My fuel injecion coversion, while turn key, was problematic and took a while to figure out that the design itself was not done well despite the money I paid for it.
All of the above required a $100.00 fuel pressure gauge to measure fuel pressure with.
I learn hard. It took a lot of diagnostic money spent before I smartened up and bought one. Never needed one with a carburetor. I saved the cost of it the first time I used it.
I'll look things up later tonight.

 

Makes sense to me. I think I might have access to a fuel pressure guage. If I do I will take a reading and post it. I will be taking a 60 mile round trip here with it today to make several errands. Will be turning it off a few times. I'll post back on how it behaves at start at those times. Looking forward to hearing from you.

 

Information obtained from general theory of oporation contained in my particular Mitchell service literature;
When engine is cold and engine speed is greater than 400 rpm the PCM operates in "open loop" mode. In "open Loop" the PCM calulates air/fuel ratio based on inputs from engine coolant temperature (ECT) senser, Intake air temperature (IAT) and Manifold Absolute Pressure (MAP) sensors. Engine will remain in "open loop" operation until Oxygen sensor reaches preset temperature AND a specific period of time has elapsed after enginee start up.
Idle Air Control Valve;
The Idle Air Control Valve (IAC) controls engine idle speed during engine load changes to prevent stalling. The IAC Valve is mounted on the throttle body or upper manifold assembly and controls the amount of air by passed around the throttle plate.
There is of course additional information.
There for I suggest at this point in time that you spend the $20.00 bucks or so to buy a Chiltans or Mitchels or whatever at your local O'Rielys, AutoZone or whatzits auto parts place that actually covers your car.
I have enjoyed being a back yard mechanic most of my life. The above means something to me, but the day of fixing things with chewing gum and paper clips is long gone. Motor fix it stuff in a can is designed to remove money from your wallet for the most part.
A dealer that tells me that they have to do $300.00 worth of Cleaning Systems to my engine or transmission when all I wanted was my oil changed and that I need to add $17.00 worth of nitrogen to my tires when cheap old air keeps them from running flat stretches my idea of respect for the dealership.
In another thread, there is discussion of a $500.00 spark plug change.
Dang, forget the dealer, bring it to my place and for $500.00 I love to change your spark plugs.
I am more than willing to expand on this information if needed. But it would help you to have some service information to read that specifically involves your car, year and model.
So I hope this helps a bit.
It sounds like there is a potential sensor problems that is sending the wrong temperature information to the PCM, the computor that keeps your engine running. I hate acronyms. The ECT, engine coolant temperature sensor, located at the end of the cylinder head on the drives side is problem prone. It could be that is defective. There are other sensors too.
The IAC valve, Idle Air Control Valve is indeed changine the idle speed which is apparently not correct.
Either
it is being told to run things too high because something thinks the temperature is too cold, or the valve is out of calibration or in some form of failure mode passing too much air or a combination of things. Or something different altogether. Which requres more research to figure it out.
Of course one must also factor into the equation, 14 years old and 200 thousand plus miles, if of course that has any bearing on things.

 

I think I will first go out and clean out the Idle Air Control Valve. Should have done it yesterday when I had the throttle control assembly off. The TCA was pretty well full of soot so I would think the IACV probably needs attention. Oh well, lesson learned. Fuel pressure was checked today and is within (lower end) specs. I have a feeling I will replace the Engine Coolant Temp Sensor as I beleive the behavior is pointing in that direction and I will justify replacing it because I am sure it hasn't been replaced..... ever. She is definately getting worn but still jusfiable in putting a little more $ into it. If I get one more winter out of it? Hey Uncljohn, thanks for your time. Appreciate it. Pete