Help! Prelude

My boyfriend has a 2000 Honda Prelude with just over 130,000 miles on it (manual). It idles horribly- it throws a code for a bad idle air control valve. Which he has replaced twice, and it did no good. I did some research and found out that it could also be the fast air control valve. Which he then replaced to no end. It is also misfiring in addition to idling even worse. He gave it a tune up and has been desperately checking for vacuum leaks…which he cannot find. He also refused to get gas at the same place because one of the codes had the option of bad gas. Nothing has helped. It sounds like it is going to explode on us and it, obviously, failed inspection. Any thoughts?! Please…(he refuses to take it to a shop)

Engine Codes: 71,74

OBD2 codes have a letter followed by 3 numbers format. The closest generic codes I can find are P0171 (fuel trim ban 1, lean) and P0174 (fuel trim bank 2, lean) One Honda specfic code with 71 as the end P1671 (TCM Data line, no signal) but I don’t think this applies. Take another shot.

He can’t fix it, and he won’t take it to a mechanic; so, how is anyone supposed to be able to help him? It can’t be done.

Your boyfriend is in deep trouble because he obviously does not have the ability to solve what could be a very simple basic problem and refuses to seek help from someone who can.

It’s unlikely the code was for a bad idle air valve but for an idle air valve out of range problem. Same goes for this “bad gas code”.

The problem is more than likely a vacuum leak and the best way to determine this is with a vacuum gauge. Poking around blindly for a vacuum leak is like looking for a needle in a haystack.

And something I always carp on; whenever an engine has a performance problem Step Number One should be a compression test. Weed out any potential mechanical problem first. A 130k miles mechanical lifter engine that has likely never seen a valve lash inspection may very well have a problem.

He’s probably spent more money throwing parts at it than if he had simply had it looked at by someone who does know what’s going on.

I read this to him he said: That the compression test will only test that the cylinder is losing compression and that he has done that (he is a mechanic just not a CAR one) and he said that if no problems are found it doesn’t mean that their isn’t one. Using a vacuum gauge to check vacuum lines will not find all vacuum leaks- for instance intake manifold gaskets. This sounds a little defensive to me but I agree he has spent way too much money here…Engine Codes on a 5th Gen honda prelude can be checked without using a scanner. They can be checked by jumping the two pronged plug underneath the one used for code scanners. Those codes are given by the CEL light flashing in sequence and then checking that sequence with a list of codes.

You are trying to help someone who knows it all, but, still doesn’t know how to find the problem. He won’t listen to you. He won’t listen to us. The best course YOU can take is: in the other direction, seriously.

Make sure your cellphone is charged . . . you’re likely to get stuck on the highway when this car craps out on you due to the ostrich approach. Ask you BF to consider asking for help beyond this site here, as we can only speculate and diagnose from what you tell us second-hand from him. Rocketman

What area do the codes you pulled related to? You do say the car is a 2000. I have a complete list of generic OBD2 codes (in letter 3 number format) and a complete list of Honda specific OBD2 codes (in letter 3 number format). This 2 number format reminds me of OBD1 format. So please tells us what the codes mean.

Leaky fuel injector(s). A little extra dribble of gas has the most effect at idle.

Codes 71 and 74 indicates misfires in cylinders #1 and #4. So check for things that can cause misfires in those cylinders. Such as a worn distributor, bad fuel injectors, etc.


My point about the use of a vacuum gauge is that it will not locate a vacuum leak but that it will simply let one know within a couple of seconds if a vacuum leak exists.
It’s far easier than eyeballing and guessing.

The compression was tested so what were the readings? People constantly post on this board about compression being good and when asked to clarify the figures they often show there is a problem. Hopefully that is not the case here.

One more question. You state it idles badly. Does this mean it runs fine at off idle speeds?

Oh I know he won’t listen to me or anyone here if he knows where this information comes from. But if I can get a better idea I can feed this information to his friend who might be able to convince him. Hah…I do one better than keeping my phone charged… I won’t ride in this thing anymore if I can avoid it. I take my perfectly mechanically sound car.

There are a lot of questions here so I will try to answer some:

The car is kinda ok at normal speeds if the engine doesn’t decide to put the check engine light on. Once the light comes on it stops keeping the speed/rpms up when you shift and drops rpms incredibly fast (he has a lighter flywheel in the thing too). When this happens shifting becomes problematic because if you don’t do it fast enough it feels like you have stomped on the brakes and it starts to buck like wild-which is why I refuse to drive it to a mechanic myself, I might push the damn thing soon though. This is only really a problem when we have to drive slow, at high speeds it is just a little rough. It also idles like it is, as he says, “camed out”- no idea if I spelled it right. We can briefly solve this problem by disconnecting the battery for a little bit but lately the check engine light will be on even when it isn’t having a small heart attack.

The codes give these options:
Misfire Detected -
Cylinder 1
Cylinder 2
Cylinder 3
Cylinder 4
Ignition System
Fuel Supply System
EGR System
IAC Valve
Contaminated Fuel
Lack of Fuel
Valve Clearance
Fuel Injector Circuit
Low Compression

And I will have to ask him what the compression test read.

I am aware that it needs to go to a shop and that people on here can only help guess, but if there is a new guess, one that he hasn’t tried, I am hoping that might help out just a little.