87 Prelude SI Idle is surging

This is my nephew's little car. He is 15 and my sister is a single mom so I'm trying to get this car in shape before he turns 16. I found it for $500 and my uncle painted it for him for Christmas but it has this surging to it and I can't figure out why. It runs great. No smoke...don't use oil or anything. It is a really cool little car. Anyway, after you start it...usually it will idle pretty high for a while then as it starts to warm up it goes into this high then low then high then low idle thing. My sister has been letting him drive it some with her in the car and he has his permit but it is an Auto and it really slams in gear if it is on one of it's High points. I need to try to fix it as they don't have the money to take it somewhere. I'm really handy with stuff and have fixed several other little problems that it had. I think it is a 2.0 FI. I had an Accord several years ago about the same year and it started doing the same thing. I fixed it myself but can't for the life of me remember how I did it. Does anyone have some ideas for me to look at?
Thanks much and my nephew Tyler also thanks you!
Rob

I have the exact same problem when it's cool out. After the engine warms up though, it goes away. I'm sorry I can't help in the fix, but I will search some other forums and let you know if I find anything! Good luck.

this is a long shot for ya, but easy enough to check. take the air intake lose at the throtle, and see if it is gummed up in there. if so, clean it out with a q tip or somthing of that nature, being careful to get the dirt out, and not in. i know that sounds stupid, but it's actually a very common problem in older GM 2.4L's, causing idling and shifting issues for the same reasons.

I'd start with checking for vacuum leaks; lines, valves...
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Not related but while yer at it, I suggest taking a look at the condition of the timing belt, if ya haven't already, don't want that to break. Good luck!

i have an 87 prelude si too, I happen to have the same problem as you, and it shifts pretty hard. Im not sure if you have the same problem, but my injectors are bad, its not cheap to fix... so i would try to find something else to look at before you put the money into them... im going to be replacing my injectors, and my o2 sensor... you might want to try looking into one of those.

Hey Everyone,
Well let me tell you in advance iwishiwasan88...it's not the FI's in my opinion! I did an injector rebuild when I fixed the fuel rail, and at least I can say it isn't that for my car anyway...
I went to AutoZone and had them order a Haynes manual for the 1979-89 Honda Prelude. They have a list of stuff that it could be... the things they tell you to check is:

Vacuum leakage
Leaking EGR valve
Air filter clogged
fuel pump not delivering sufficient fuel to the carb or fi system
leaking head gasket
timing belt and/or pulleys worn
camshaft lobes worn

I will check it out and let you know what's up.

Well im glad there was someone else with that problem... lol... so that i dont have to put the money in to my injectors if i dont need to... cuz they arent cheap... they are leaking... but im not too worried to the point that i want to spend the money on them... so if there is something else, than thats coooooool. Maybe. as long as its cheap. lol. I have already replaced my air filter, and checked for vacuum leaks... but came back with the same problem... except with my car, its been surging AND puttering.... puttering to the point it turns off (only once) until you put the car into gear, and then your all set. But the time it turned off, it decided it didnt want to go faster than 35mph, and when we finally did it didnt want to go slower than 45mph... so maybe (not sure) my problems are related... do you have any suggestions to offer my second problem??? lol... thanks.

Hey iwish,
I really think that you should start with a FI rebuild kit for your four injectors. I did it, it's only about 5 bucks total, for a bunch of o-rings, and clean the hell out those injectors once you remove 'em. It fixed mine, and mine were pretty messy.
In regards to the second problem, I'd say it's all related to insufficient fuel into the engine. What you can do to troubleshoot is pretty easy. You need a voltmeter...Warm up the engine to normal temp. Just disconnect one FI at a time. If the idle changes equally among all four, then they're functioning OK. If unplugging one doesn't change the idle, or changes less, etc...then check the voltage on the injector electrical connector. If the voltage fluctuates between 0-2 V then replace the injector. If there's no voltage, then check the wiring between the resistor and the injector and between the injector and the ECU for a short, break in wire, or bad connection... there's more if there's no resistance. If that's the case, re-post and I'll do it as well.

Good Luck!

if your idle surges until it gets to operating tempture it's most likely your fast idle control valve it's on the back of the intake manifoild by the firewall it has 2 coolant hoses on it , if if doesn it after it warms up also i would check the idle adjust screw screw ont he throttle body and make sure it didn't back out as that can cause a idle problem

I had the same problem tighten the air valve on the intake manifold mine was on back but on that gen I think its on top of the manifold good luck tell us what happens.

I don't know if you have considered this or not but it takes a second to do, belive it or not but when air gets into the cooling system it can cause a surging idle even when the car is warm. There should be a bleeder valve on the thermostat houseing, just loosen it with the car running and let the fluid come out till it just flows out without any breaks in the fluid retighten the valve and it may fix the problem.

I had an 89 that did the same but i would also do it after runnin down the highway for a while then stopping for traffic...i was getting all kinds of codes from the computer so i took it to a shop and they checked all my sensors and they were all good...turns out i had a bad comp. it burnt up somehow...they couldnt tell me how but after the replacement it ran like a champ...set me back about 500 bucks though...but most of it was diagnostics