Is it normal for an L98 when right after start up (cold or warm) the idle rises to nearly 2000 rpms and then just settle at 700/800? This all happens in just a second. The idle sometimes goes up and down between 800/1100. Cleaned iac and checked tps, all fine, no codes, only the one for the egr but maybe that´s just the problem here. I noticed the engine runs much smoother and responds better to throttle change after iac cleaning and changing out the thermostat because that one was stuck in open pos. Now the engine warms up like it should. Can this (new thermostat) have a positive effect on an engine running much smoother?

 

The "idle" RPM on a L98 engine is directly related to the temperature of the engine coolant. Here is the table that is programmed into the ECM on my 89 engine:

Idle RPM vs. Coolant Temperature

Deg F RPM

306 575.00
284 575.00
262 575.00
241 575.00
219 575.00
198 575.00
176 575.00
154 600.00
133 600.00
111 750.00
90 900.00
68 950.00
46 1050.00
24 1050.00
03 1050.00
-18 1050.00
-40 1050.00

Now....you must realize this assumes all sensors and related wiring circuits are in working condition. Hope this answers your question.

 

That I understand, Bob. But this is what happens: I turn the key, the engine fires up immediately and while it fires up it jumps up to about 1800/2000 rpms. I have another injection car here that doesn´t do like that. I can understand if it fires up that it jumps up to a 1000/1100 or so and then settle for 700/800 after a second or so but it seems here like someone has been pumping gas in the engine right before cranking. And no other problems with cold or warm start. Put in new injectors as suggested a while ago. Can´t recall if this situation was allready there before injector swap.

 

Theo: The real question I have is.....how is the engine getting the fuel to run at approximately 2000 RPM at start up? My first thought was leaking injectors! However, you would have to experience multiple fuel leaks to have the engine start as you describe. Does the car always start like this? Being more specific, if you shut off the car while it is at operating temp, wait 15 minutes and restart....what happens? What happens if the car sits overnight, does it still start and run at 2000 RPM? Know anyone with a scan tool in your area? Sorry that I cannot offer more info to you on your problem.

I am eagerly waiting for spring as it is very cold in the St. Louis, MO area. I am sure you have a different definition of cold in your location

 

I let it sit overnight and started and it would only go up to let´s say 1500 and go down almost immediately to +-800. I shut it off at op. temp and started after 15 min. and it would go up to +-1900 and go down again and settle at +-800, seems OK. I just wonder how they act when they are new from factory, does it run 800/900 directly after start or do they increase a little in rpms as well (for half a second tops). Outside temps are around 40 F right now, maybe that has something to do with it. I changed to a new thermostat (180) because I thought the old one was at fault but it might have been a 160 in it. Car was originally sold in Florida in ´91. But I don´t think they have put in another chip or so. Everything is stock, no mods at all. It even has the original exhaust (2 of 4 pipes working). Only thing I did was remove frisbee. Serves another purpose now being a coaster for a flower pot outside in the garden.

 

Theo: Now that I read your last post, how can the RPM jump to 1500 to 1900 for one half second as you cannot read the RPM that quick? My 89 had a strange habit in that the crank seemed to rotate about 3-4times before it would start. I then found out that the ECM was programmed to "wait" for 8 spark pulses before the plugs would fire. The injectors were firing and no spark. The car would start up and run fast for a short period of time. Does your car seem to take a few seconds of cranking before it starts.....regardless of the coolant temp?

 

Starts right up when cold, takes maybe one second when warm but not more. So I guess it can´t be the injectors, but that doesn´t mean the injectors are A OK. Could a minor difference in ohm between the 8 "jec´s" be doing this. Haven´t checked them now. I did that though when I put them in (the shop that is) for almost a year ago. Then there is this situation where the ECM must learn al the sensor settings again after the battery has been disconnected.

I have been playing with the TPS. I know they are not adjustable but when I tested it the TPS showed 0.63 volts at idle, unscrewed the torxes a little and while I had the probes connected I turned it a little untill it showed 0.54 volts, then at WOT it showed around 4.5 volts. This all according to the write up I found here on the forum. There is very little play in the TPS even with the round mounting holes in the TPS. And yes, I disconnected and reconnected the single wire found just under the wiper motor as described. IAC and TB are clean and working.

So to make a long story short. ECM as you suggested? Or maybe the "jec´s" after all, I will ohm check them again and post what I find both cold and warm.

 

A non adjustable TPS means just that and most read .62 volts. If you've broken it - replace it.

When the engine is shut off, the Idle Air Control Motor retracts the Pintle so the right amount of air gets through the throttle body to match the extra squirt of fuel the ECM pulses through the injectors for a quick restart. Restart rpm should be higher than shutdown rpm, but return to what it shutdown at within a couple of seconds. If you hooked up a scanner, you would see the Parked or Retracted Position of the Idle Air Control Motor at something around 160 counts (or a % number if it's '96 or above) and once started, those counts would drop to match whatever the ECM is targeting as an idle speed until the actual Idle Speed is within 50 rpms of Targeted (Drive) or 100 rpms of targeted (Park/Neutral). I'd guess that yours operates no differently and is trying to do that - extend the Pintle to reduce air to reduce idle speed - only it can't because the Pintle is stuck or the Idle Air Control Motor is bad. I'd start with a scan where you can not only see what the Idle Air Control Motor is doing, but also the Coolant Temp and probably just as importantly, verify that the Tach readout from the
Dash is accurate. Once you've got some info, decide the best course to fix it - probably a thorough cleaning of the throttle body and/or a new IAC - but without scan data, it's only a guess.

 

Now that´s cool info about this 0.62 volts. Haven´t read about that in my FSM. I don´t think I broke it, just "adjusted" it but I think I can get it back to 0.62 volts. I´ll check if someone has a scanner here or else I will have to buy one myself. Could these be used on a 1999 Hyundai Elantra as well, if it´s a obd I/II scanner?

 

There have been mixed reviews about Scanners working for both systems. Auto XRay seems to be the best at recognizing either. I use dedicated scanners depending on system so I have no experience with it.

 

Put the TPS back to 0.62 volts and ohm tested the "jec´s". Five were 14.4 ohm, two were 14.3 and one was 14.7 ohm cold. Warm they all show +/- 0.5 ohm higher arround 15 ohm , shouldn´t they ohm 16.5 or so?

 

Theo: "IF" you have stock Multec injectors, the resistance should be 16.5 +/-.3 ohms when COLD. I would bet you do not have stock injectors in your car given the readings you posted above. Here is what the stock Multec injectors look like:



Let us know what you find on this.

 

Nope, I have replaced them with "new" ones. They are marked "ford" and are cleaned ones. Bought them of ebay. F55E-A2D or A2E, don´t recall wich ones. Came from injectors4u. Have been in there for half a year now. Engine runs smooth, responds well. I think it is a vacuum leak of some sort. A very little one, because I can´t find anything. Not even when I try with a spraycan with injector cleaner. No idle increase what so ever.