Prelude won’t idle

[Cris]

I read the troubleshooting page about how to solve an idle problem and I’m still stumped. I have a 1994 Prelude Si H23A1 Automatic and long story short, it has a problem with idling. So a while back I noticed a hesitation from a stop, the RPM’s would be sluggish then the car would pick up speed. My water pump started to leak, so I replaced it as well as the timing belt. Once back I noticed I had more power, later that night my idle got really rough, but ran great above 2k RPM. I noticed the mechanic left the throttle open to keep it from stalling, he told me to change the throttle body, so I got a used complete OEM one. So new TPS and FITV. The TPS was replaced before and had a rough idle and it would get low and stall once at operating temperature. Before the timing belt job it would idle rough and low, but after this it would idle really really rough, the tension on the belt is nice and tight, but not so tight, just right. After the new throttle body was installed, the car came out worse, more hesitation and sluggish acceleration. If the throttle plate is closed the car would die unless I give it gas, so it was kept open, he said my IACV was bad, so got a used OEM Denso unit. He put it on and lol throttle still needs to be kept open. It runs better but still has that sluggish acceleration throughout all the RPM ranges. Sometimes it would accelerate normal others sluggish. I noticed in park or neutral the idle would be like at 1k rpm, but as soon as I pop it in park or reverse I can hear my cold air intake sucking in the air and the idle climbs to 1300 or so and stays there. I know Eric you said if the ECU can’t see the TPS is closed it’s not a good thing, maybe my ECU needs to re learn to idle? I have no CEl I even jumped the connector and no codes. Btw before the timing belt change if my alternator was unplugged or the old TPS at idle it would idle smoother and the idle wouldn’t go down to almost stalling. I doubt my MAP sensor or O2 sensors are bad since I have no CEL. I will check for a vacuum leaks tomorrow since It’s been a month since I last checked them. But any advice?

Topic

[dan]

eric has a very… valid point. your mechanic rather than take the time too diagnose the issue has instead thrown parts at the issue, this can in some cases make things worse.

[Cris]

Before all this the car would have a rough and low idle, It would idle smoother if the alternator connector was unplugged. I remember about almost a year ago I was driving with a buddy of mine to a restaurant when my CEL came on, When we got there I shut it off and turned it back on, The CEL never came back on. Later I jumped the service connector and got a Code 20 ELD stored in there, but I reset the computer after the CEL came on but a code never came on indicating a Code 20 till I jumped it like 3-4 months later, ECU didn’t think it was a big deal maybe?. I replaced the whole fuse box assembly with no change, but now I wonder if that CEL that came on and never came back had something to do with my idle problem. The TPS was messed with before, but now it has a whole new untouched TPS on it via new throttle body. Before it idled fine no problems, but it did stall once at operating temp, but it is way worse now. Is it possible that the mechanic maybe damaged my ECU? He knows it’s not right to leave a car like that, but he didn’t tell me nothing when I got it back after he changed the IACV. I’m gonna give it one last try and reset the ECU and see what happens.

[EricTheCarGuy]

ECU problems on Hondas are VERY rare. I wouldn’t go there unless you had eliminated all other possibilities. If you’re vehicle has an electrical issue it can effect the performance of the engine, especially at idle. You might want to check the battery and alternator to make sure they are functioning correctly.

http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

That said, all the work your mechanic did is suspect. Not only because it was bad practice, but also because it adds to the list of possible causes. It would be much easier to help you diagnose this if we knew those systems he messed with were in order. The idle article I wrote was VERY thorough about this. I spent a lot of time putting it together since idle problems are a popular topic. There are also SEVERAL things that can effect idle that are covered there. I suggest you read through it again and follow the steps as it may lead you to the problem. Otherwise, I would suggest taking it to someone that is familiar with working on Hondas.

http://www.ericthecarguy.com/faq/solving-automotive-idle-problems

Keep us posted.

[Cris]

I will read it again and will check everything step by step.

[Author]

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