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1992 H23 engine rpm all over the place

 
Old 04-10-2019, 10:48 PM
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Default 1992 H23 engine rpm all over the place

Hi! I have a 1992 H23a1 Prelude (automatic) that wont stay on. When the engine is started the rpm go wild, as in, it jumps back and forth in an unpredictable manner, for example, it goes from 0 to 2,000 then down to close to 1,000 then jumps up to 2,500, then goes down to 450, and so on until it stalls. If I try to put it in gear it just stalls. It has an exhaust leak in the manifold-downpipe connection (before 02 sensor). The problem started after I was finished replacing it's head gasket, took it out for a quick check and it stalled after I fully pressed the throttle going up a hill, after that it wont stay on. Also worth mentioning that after torquing the manifold-downpipe connection, the car idled on 1,500 rpm for a minute or so, then the rpms let go again. Any help is much appreciated! Thanks!

Last edited by elpollo; 04-10-2019 at 11:22 PM. Reason: Minor corrections
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Old 04-10-2019, 11:16 PM
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Default Re: 1992 H23 engine rpm all over the place

Forgot to mention, the spark plugs form carbon build up on the tips
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Old 04-11-2019, 02:27 AM
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Default Re: 1992 H23 engine rpm all over the place

Originally Posted by TimiK
quick what to do list

usually these things fix bad idle or/and hesitations:

- new spark plugs & wires
- new distributor cap & rotor
- new air/fuel filters
- clean injectors/iacv/egr/fitv
- bleed the coolant
- new pcv
- adjust valves and ignition
- adjust idle from tb's screw and throttle cable
- check does sensors work properly: map, iat and tps (and try calibrating tps)
- then check wires, connectors and hoses, check grounds
- check ICM and ignition switch (there was 5th gen repair call for this also)

-check o2 sensors and vacuum/exhaust leaks (check all the seals - IM/header/TB gaskets, injector seals, maybe even buy valve cover gasket set...)
-check timing. after that: double check timing
-is engine light on? check error/engine light codes
-clogged cat might you give some trouble as well (usually when driving) - check cats condition

if none of these seem to work - do compression and leak tests
and if you have chipped ecu and youre running it just with basemap, it might not work as well than properly tuned one

those are basic maintenance as well.

Last edited by TimiK; 04-11-2019 at 08:34 PM.
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Old 04-11-2019, 05:44 PM
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Default Re: 1992 H23 engine rpm all over the place

check for vacuum leaks.
check for moisture on the spark plugs that could indicate the HG is not sealing.
check for any stored trouble codes.
make sure coolant is full.
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Old 04-16-2019, 10:49 AM
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Default Re: 1992 H23 engine rpm all over the place

Thanks for the list! I've already checked most, the only things I haven't are the sensors (map, iat, tps, and o2). How would one verify their functionality? Using a multimeter? Also, does an exhaust leak after the exh manifold count as a meaningful vacuum leak?
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Old 04-16-2019, 10:54 AM
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Default Re: 1992 H23 engine rpm all over the place

Originally Posted by motoxxxman View Post
check for vacuum leaks.
check for moisture on the spark plugs that could indicate the HG is not sealing.
check for any stored trouble codes.
make sure coolant is full.
The spark plugs are dry, hey just form carbon on the tips. Would an exhaust leak count as a meaningful leak? In regards o the code, it did throw the one for the coolant sensor, apart from that it's supposedly clear. I checked the codes using the paper clip in the plug and morse code kind of thing in the check engine light method.
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Old 04-16-2019, 11:10 PM
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Default Re: 1992 H23 engine rpm all over the place

Originally Posted by elpollo View Post
Also, does an exhaust leak after the exh manifold count as a meaningful vacuum leak?
no, it count as meaninful exhaust leak which mess with your o2 sensor

also you should replace that sensor which gives you that code
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Old 04-17-2019, 08:58 AM
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Default Re: 1992 H23 engine rpm all over the place

Originally Posted by TimiK View Post
no, it count as meaninful exhaust leak which mess with your o2 sensor

also you should replace that sensor which gives you that code
Ok. I'll buy the sensor, install it and see what happens. I would really like to diagnose the o2 sensor but I'm not sure how. (I bough new bolts for the pipe and installed two of them because one of them wasn't accessible at the time, although there is still a slight exhaust leak, its much better than before). Are there any obd 1 scanners for the 92 prelude? I've only seen one, but I'm not sure if its legit.
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Old 04-22-2019, 01:20 AM
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Default Re: 1992 H23 engine rpm all over the place

Originally Posted by elpollo View Post
Ok. I'll buy the sensor, install it and see what happens. I would really like to diagnose the o2 sensor but I'm not sure how. (I bough new bolts for the pipe and installed two of them because one of them wasn't accessible at the time, although there is still a slight exhaust leak, its much better than before). Are there any obd 1 scanners for the 92 prelude? I've only seen one, but I'm not sure if its legit.
Just jump the service connector to pull the codes. Fix the sensor issue first. I thnk you have a vacuum leak, Check all hpses connected to the intake manifold. When you put back the inatke gasket was it in a good shape?
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Old 04-22-2019, 10:49 AM
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Default Re: 1992 H23 engine rpm all over the place

Originally Posted by hondamyheart View Post
Just jump the service connector to pull the codes. Fix the sensor issue first. I thnk you have a vacuum leak, Check all hpses connected to the intake manifold. When you put back the inatke gasket was it in a good shape?
When I put it back together I bought new intake and exh gaskets. From what I could see, all the hoses were fine. To diagnose this, should I pump some smoke through the intake?
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Old 04-22-2019, 10:54 AM
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Default Re: 1992 H23 engine rpm all over the place

I could shoot a video of how the car starts and "runs" and upload it, so you guys can get a better idea of the problem
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Old 05-09-2019, 02:18 PM
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Default Re: 1992 H23 engine rpm all over the place

Just an update... Brought someone over to check the car, and apparently it doesn't have a vacuum leak, also the cat was eliminated by the previous owner, so it should start without the o2 sensor. The sensors seem alright so that most likely isn't the problem. The timing is ok too, although he adjusted the ignition a bit and the car stayed running instead of stalling, but the rpm were still erratic and it kinda wanted to stall a few times (it did once while he was checking it). He recommended I check the fuel system, according to him, it might be a bad fuel pump or filter. Could this cause carbon buildup o the spark plugs?
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Old 06-03-2019, 05:42 PM
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Default Re: 1992 H23 engine rpm all over the place

Update: The fuel filter was full of rust and apparently the stock filter was changed for a universal one, so the lines are different. Haven't done anything to the car in a while, kinda gave up on it.
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