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Discussion Starter · #1 · (Edited)
So the car idles strangely only from cold start. Once it's up to temperature it idles steady around 750.

The only anomaly was yesterday. I started it cold and allowed it to warm up for about 5 minutes. Then i pulled it back to shut the gate and thinking it was in neutral dropped the clutch, idle had been surging the entire time. Engine died but when I restarted it the surging idle was gone.

Could be coincidence idk.

Anyway first i replaced the PS line, 02 sensor, spark plugs, and cleaned the airfilter to address error codes. (there are none at the moment, 02 & TPS was on but went away after ecu reset)

Then a few days later I installed an aftermarket TW sensor and bled the coolant, to address idle this did not fix the it and i swear it idles worse now. More likely to surge and once its warmed up it seems off. It makes this whiney noise every once in a while but maybe its just the radiator fans weren't working before. Unfortunately the stock TW (thermal water) sensor broke on removal.

Anyway the idle surges up to 2400~ and back down low over and over. Sometimes a bit after start, sometimes right at start, sometimes not all, sometimes it just idles down and dies if i don't hit the accelerator. Even if its 80 degrees f outside the car was run an hour before it still does this sometimes. Once the coolant dial goes up an 1/8th it stops and goes down to normal.


Do you think its the wax expansion ring or vacuum leak?

Wouldn't a vacuum leak cause problems even at operating temperature? I can shift into neutral on the freeway and it idles just where it should.

p.s. can anyone recommend a good 02 sensor?


1990 Prelude Si 4ws b21a 2.1L
 

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There is not one good o2 sensor many brands are good. We used to have problem with bosch but that was years ago and they are reported good now. NTK are good, Wagner, Nippon denso others that I am forgetting. Amazon has a brand cheap price wise. I forget which brand. Beck arnley would be if they still make one.

I would suspect it is your fast idle valve. You can get a replacement on http://rockauto.com . You can confirm by putting a cereal bock like cardboard block off in between it and the fiv and intake manifold to block it off. If that fixes it then that is your problem. I also have done everthing but buy and confirm a good permanent block off plate on ebay for a decent price.

It is also possible that the coolant isn't totally bled. It takes a long time and may take more then once. You should also have the heat slider all the way to hot inside the car when bleeding to make sure the heater core is bled and full preventing a good coolant system bleeding.
 

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Discussion Starter · #3 ·
There is not one good o2 sensor many brands are good. We used to have problem with bosch but that was years ago and they are reported good now. NTK are good, Wagner, Nippon denso others that I am forgetting. Amazon has a brand cheap price wise. I forget which brand. Beck arnley would be if they still make one.

I would suspect it is your fast idle valve. You can get a replacement on http://rockauto.com . You can confirm by putting a cereal bock like cardboard block off in between it and the fiv and intake manifold to block it off. If that fixes it then that is your problem. I also have done everthing but buy and confirm a good permanent block off plate on ebay for a decent price.

It is also possible that the coolant isn't totally bled. It takes a long time and may take more then once. You should also have the heat slider all the way to hot inside the car when bleeding to make sure the heater core is bled and full preventing a good coolant system bleeding.
Thanks for the great info :smilejap: I hadn't read that the heater should be cranking to do a coolant bleed.

How long should i leave the bleed screw open for do you think?

I meant to ask can you recommend a good TW sensor (coolant temp next to thermostat) cause the autozone one i bought seems worse that the old one.
 

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I hadn't read that the heater should be cranking to do a coolant bleed.

How long should i leave the bleed screw open for do you think?
Heater should be all the way in the red but the fan should be OFF for bleeding.

Here's what you want to do:

Crack bleeder screw open, fill radiator with coolant, close bleeder. Turn on car, run engine at 2-3000RPM for 2-3 mins, crack bleeder open until it drips, close it, wait until fans kick on and then fill the radiator/check the level, crack bleeder until it drips, rev car to 5k RPM with bleeder open for 5 seconds, close bleeder, let car idle, fill coolant again, put cap on radiator and turn off car.

Let the engine cool, remove cap, fill if needed, put cap back on and drive until car warms up, stop car when it warms up, crack bleeder until it drips, add coolant.

I would do this, and then from there, see if that fixes the problem.
 

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Bouncy idle when cold is probably the TW sensor or TW sensor wiring still. I would do the test procedure in the manual to check that it is working correctly.

It's bouncing because the ECU thinks the car is at operating temp when really it's not and the FIV is still open.
 
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