Bushwack Posted February 4, 2022 Share Posted February 4, 2022 Hi Folks, I posted this question on FB. But in case some do not log participate in the FB forum,... Just bought a '90 coupe and I never had this problem: At 86,000 miles, the engine runs well but intermittently, whether hot or cold, the engine will rev to 2500 RPM and not decrease RPMs. There are times I'll get a normal cold start (1,200 RPM and eventually settles to 800 RPM). There are times I'll get a normal hot start. And there are times it gets to 2,500 RPM and stays there. Putting the transmission into gear does not bring the car down to a normal idle. I've changed the idle control valve (twice), clean the fuel injection - the engine will still rev intermittently at 2,500. Any suggestions on fixing this problem is appreciated. Thanks. Link to comment Share on other sites More sharing options...
2seater Posted February 4, 2022 Share Posted February 4, 2022 The first thing to check is the TPS voltage, ED01, in diagnostics. Should be .38-.42v. I just had one last summer that had an erratic idle and found the TPS voltage high and when trying to adjust it, the voltage would bounce all over. In short, the TPS was going bad. Could be other things but start there. Easy and free to do 1 Link to comment Share on other sites More sharing options...
Bushwack Posted February 4, 2022 Author Share Posted February 4, 2022 17 minutes ago, 2seater said: The first thing to check is the TPS voltage, ED01, in diagnostics. Should be .38-.42v. I just had one last summer that had an erratic idle and found the TPS voltage high and when trying to adjust it, the voltage would bounce all over. In short, the TPS was going bad. Could be other things but start there. Easy and free to do TPS....Throttle position sensor??? Link to comment Share on other sites More sharing options...
2seater Posted February 4, 2022 Share Posted February 4, 2022 2 hours ago, Bushwack said: TPS....Throttle position sensor??? Yes, and the .38-.42v is at idle position. It should increase smoothly to over 4 volts at full throttle. 1 Link to comment Share on other sites More sharing options...
D-a-n-i-e-l Posted February 5, 2022 Share Posted February 5, 2022 Check for a vacuum leak. They can be intermittent and a pain to find. 1 Link to comment Share on other sites More sharing options...
PABrady Posted February 16, 2022 Share Posted February 16, 2022 My Reatta has rich burn smell in closed loop, gets bad gas mileage and sort of backfire or pops sometimes under hard acceleration when you let off the gas. Thanks to this tread I decided to check my TPS voltage and its at .134 Volts at idle. I assume it can be adjusted. Not sure how to do that. I messed with it once so it's probably not installed correctly. Just loosen the screws and move it a little? Thanks! Link to comment Share on other sites More sharing options...
D-a-n-i-e-l Posted February 16, 2022 Share Posted February 16, 2022 O2 sensor. 1 Link to comment Share on other sites More sharing options...
2seater Posted February 16, 2022 Share Posted February 16, 2022 12 hours ago, PABrady said: My Reatta has rich burn smell in closed loop, gets bad gas mileage and sort of backfire or pops sometimes under hard acceleration when you let off the gas. Thanks to this tread I decided to check my TPS voltage and its at .134 Volts at idle. I assume it can be adjusted. Not sure how to do that. I messed with it once so it's probably not installed correctly. Just loosen the screws and move it a little? Thanks! Yes, loosen mounting screws and rotate to .38-.42v. Does it increase with throttle as it is now? I don't remember ever seeing one that far off unless there were other issues. 1 Link to comment Share on other sites More sharing options...
PABrady Posted February 17, 2022 Share Posted February 17, 2022 Ok I adjusted it to .400 volts and at full throttle its at 4.20 volts (4.22 with the floor mat removed). Is that too much? Perhaps I should of set it to .380. I will look into the O2 sensor as it still has that fuel rich smell when you first start it. Too much snow/salt for a test drive. There are no codes. Thanks Link to comment Share on other sites More sharing options...
2seater Posted February 17, 2022 Share Posted February 17, 2022 10 hours ago, PABrady said: Ok I adjusted it to .400 volts and at full throttle its at 4.20 volts (4.22 with the floor mat removed). Is that too much? Perhaps I should of set it to .380. I will look into the O2 sensor as it still has that fuel rich smell when you first start it. Too much snow/salt for a test drive. There are no codes. Thanks The TPS range sounds like it is spot on now. The ECM must learn the new parameters now that the sensor has been corrected so it will take a little time for it to adjust. Even better is to disconnect the battery ground for a couple minutes to force the ECM to start over and learn from scratch. In any case, It really needs to be driven for a while for changed settings to be accommodated. A new O2 sensor as suggested is always a good idea if the existing ones history is unknown or you are chasing a mileage issue. It is usually a good idea to make one change at a time to see the effect but the O2 replacement is an exception. 3 Link to comment Share on other sites More sharing options...
Bushwack Posted February 17, 2022 Author Share Posted February 17, 2022 As the OP, here's a follow up: Mechanic determined the reason the RPMs are inconsistent (very low on a cold start and high when hot), is the ECM is not sending a signal to the IAC. Mechanic thinks the problem is the ECM (the TPS, O2 sensor, and MAF are good). There were two vacuum leaks that have been repaired. He did re-install the TPS. Questions... the problem still persists. Because the TPS was reinstalled, should I drive the car for 10-15 miles so the ECM can 'adjust' (is this necessary)? Is there something else to look at? *I* would think the ECM would be consistent - either it sends a signal or it does not. Could the ECM be the problem? Link to comment Share on other sites More sharing options...
Ronnie Posted February 17, 2022 Share Posted February 17, 2022 Perhaps the ECM is getting an erroneous signal from a sensor (sensor info may be sent to the BCM first and then relayed to the ECM) that is telling the ECM to raise the RPM to offset an extra load on the engine. Most likely suspect would be the pressure sensor on the power steering rack is bad. Other Reatta owners have experienced this problem. Should be easy to check using onboard diagnostics. I don't think it is likely a bad ECM is the problem but it's possible. 1 Link to comment Share on other sites More sharing options...
2seater Posted February 17, 2022 Share Posted February 17, 2022 Any time things are changed or adjusted, the ECM may need time to fill in the desired settings, so driving it under varied speeds and loads is a good idea. You can sometimes see the difference by disconnecting the battery so the ECM starts over from its base programming. It may run better or worse for a bit until it fills in the blanks. As Ronnie alluded to, sometimes a sensor is out of range enough to cause the ECM to adjust, but not out far enough to set a code. That is much of the reason as a test to sometimes disconnect a sensor, like the MAF for example, which forces the ECM to substitute a programmed safe setting. It is possible for an ECM to be bad, but not common. Link to comment Share on other sites More sharing options...
Bushwack Posted February 17, 2022 Author Share Posted February 17, 2022 (edited) Thanks folks. I think what I will do is disconnect the battery, let the car sit overnight, re-connect the battery and take the car on a 20 mile drive of both highway and stop-n-go traffic. Afterwards, I'll pull codes and see what we find. Edited February 17, 2022 by Bushwack Typo (see edit history) 2 Link to comment Share on other sites More sharing options...
Bushwack Posted February 20, 2022 Author Share Posted February 20, 2022 (edited) So... this morning I reconnected the battery and the car had difficulty maintaining idle (had to help it get to 1200 RPM to warm up). After a few minutes, idle was at 700-800 RPM. I took the car on a 25 mile drive of mixed city/freeway traffic. I noticed when I got off the freeway to return home, idle was at 1600 RPM when in neutral (the car felt like it was pulling as I came to a stop). I returned to the freeway to go home, eventually got off the freeway after another 8 miles going between 55-70MPH, and idle was normal at 600-700RPM. A trusted mechanic who no longer has his shop mentioned I have two separate problems. The cold start problem (he suggests to replace the cold start valve - isn't that the IAC?). For the high idle, check for vacuum leaks (there are no vacuum leaks). Might also be a throttle body issue, but he said that should be a last resort. The IAC and TPS have been replaced (and set to specifications) and there are no error codes. I would think if a vacuum leak exists, idle would always stay high and not return to normal after 20 minutes. Before replacing the ECM (as some have mentioned because of the idle fluctuations), I still think the issue is something else. ...and if I was mechanically inclined, I wouldn't be posting this - asking for advice. 😁 Edited February 20, 2022 by Bushwack added additional information (see edit history) Link to comment Share on other sites More sharing options...
2seater Posted February 21, 2022 Share Posted February 21, 2022 I am somewhat out of ideas at this point, but even though it does sound obvious, you should check that there isn't some sort of throttle cable anomaly causing the throttle to hang up at times. When it is in one of its high idle moods, just manually check the arm under the hood to be sure it is in closed position. The other item to watch is the IAC counts in diagnostics. You need to sort of develop a feel for this one as it isn't a static number. The counts will increase when you open the throttle so it is ready to catch the engine and let it down smoothly if the throttle is snapped closed and you can watch the counts as the engine warms up where they should slowly decrease to bring the idle down. Once you have a feel for what the counts are at a good warm idle, you can see if they are out of that range when it acts up, either high or low. If you are familiar with diagnostic overrides, you can manually close the IAC from the driver's seat to see if the idle can be forced lower by overriding the IAC. 1 Link to comment Share on other sites More sharing options...
ChrisWhewell Posted March 8, 2022 Share Posted March 8, 2022 Maybe the data going to the engine is b/c a sensor or system is telling the pcm that the ambient air temp is very cold, and it is running in fast idle cam mode. Although, 1600 revs is a bit high maybe for that interpretation. Vac leaks always 1st suspect. Maybe consider to spray a little water mist around engine when its running and if vac leak, then it should cause a change in revs when misted. Does the transmission have a vacuum modulator ? maybe a hose is cracked Link to comment Share on other sites More sharing options...
ChrisWhewell Posted March 8, 2022 Share Posted March 8, 2022 On 2/20/2022 at 7:23 PM, 2seater said: I am somewhat out of ideas at this point, but even though it does sound obvious, you should check that there isn't some sort of throttle cable anomaly ....... True !! I had that more than twice. Some graphite spray is nice, although they probably have a newer lube for that by now. Link to comment Share on other sites More sharing options...
Bushwack Posted March 8, 2022 Author Share Posted March 8, 2022 UPDATE: Problem resolved. After lots of troubleshooting and at last resort, the ECM was replaced (thanks Jim Finn), moving the old PROM to the 'new' unit, and life is good. Car idles at normal temperature when in gear slightly higher then I'd like (800 RPM, I think normal is 650-750). Nevertheless the car now drives as well as any Reatta I've owned. In retrospect, maybe I didn't need to have the IAC or TPS replaced. But assuming they were original and not too expensive to replace,... Thanks everyone for your input 4 1 Link to comment Share on other sites More sharing options...
Olyeg Posted March 8, 2022 Share Posted March 8, 2022 Congrats man I bet it’s a great feeling having her back on the road without worry. 1 Link to comment Share on other sites More sharing options...
PABrady Posted March 15, 2022 Share Posted March 15, 2022 My Reatta is running better as well the little I have been able to drive it. Found this informative Know How video I recommend watching if you haven't already. However, I don't know what to make of the TPS voltage being a wider range. Assuming all LN3 years are the same. Perhaps I don't understand what they mean by Closed Throttle or perhaps they are talking about TBI Mode maybe the test equipment involved? Link to comment Share on other sites More sharing options...
2seater Posted March 16, 2022 Share Posted March 16, 2022 Maybe there was a running change in the TPS recommendation? That is such a huge range I don't know how that would work but I was curious how our tribal knowledge came to .38-.42 for idle setting. According to my 1990 FSM, the acceptable range is .33-.46, a bit wider than we generally use as a guide but further along, in the section dealing with part replacement, it does recommend .38-.42 for the setting on installation as it is in the center of the acceptable range. Of course, I noticed it also made the point that if there is either code E021 or E022, the ECM will generate a substitute signal for the TPS and it will also have a high idle. Link to comment Share on other sites More sharing options...
Bushwack Posted March 16, 2022 Author Share Posted March 16, 2022 11 hours ago, 2seater said: Maybe there was a running change in the TPS recommendation? That is such a huge range I don't know how that would work but I was curious how our tribal knowledge came to .38-.42 for idle setting. According to my 1990 FSM, the acceptable range is .33-.46, a bit wider than we generally use as a guide but further along, in the section dealing with part replacement, it does recommend .38-.42 for the setting on installation as it is in the center of the acceptable range. Of course, I noticed it also made the point that if there is either code E021 or E022, the ECM will generate a substitute signal for the TPS and it will also have a high idle. Excuse my ignorance, but would the higher setting make for a higher idle? If the setting was .33 - .38, would the idle be lower then the recommended .38 - .42? Link to comment Share on other sites More sharing options...
2seater Posted March 17, 2022 Share Posted March 17, 2022 14 hours ago, Bushwack said: Excuse my ignorance, but would the higher setting make for a higher idle? If the setting was .33 - .38, would the idle be lower then the recommended .38 - .42? I honestly don't know but it does seem to be implied that it might be the case. I would think that it wouldn't permanently change the idle, but it might affect it until the ECM learns the new normal? Sort of like the fuel integrator and block learn. The ECM can adjust the fueling to maintain the desired mixture but it has only limited ability to do so and needs to be in a range that it can adjust for. 1 Link to comment Share on other sites More sharing options...
padgett Posted April 1, 2022 Share Posted April 1, 2022 So far no one has mentioned the IAC (idle air controller), they often stick causing a high idle. See here. Link to comment Share on other sites More sharing options...
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