Idle Problems in CRX after trans swap

[GasSavers_bobski]

The O2 value and air/fuel ratio oscillates like that under normal operation. The O2 sensor actually detects a very narrow range of values (something like 14.5:1 to 15:1, so when the ECU makes a small adjustment to the mixture, the O2 reading will swing from one extreme to the other. The ECU isn't able to peg the center ideal reading on the O2 sensor, so it's constantly adjusting and re-adjusting.

Is the spring still in place on the idle adjust screw?

The PCV valve is a metal fitting screwed into a port on the intake manifold between the 2nd and 3rd cylinder runners, next to the intake temperature sensor. It should have a U-bend tube attached to it that runs down between the 2nd and 3rd runners to the breather box on the back of the engine block.

[GasSavers_Hal9000]

Bobski, the spring on the idle adjust screw is still in place, but what difference would that make?

Also, we confirmed this morning that the extra air is definitely coming through the ICV, so that pretty much eliminates the PCV as the major cause as far as I can tell...

Anyway, I thought I had the problem solved, but alas! No luck....

This morning I tested the temp sensors, they're both good and in range. When I checked the TPS on an oscilliscope though, it was pretty wacked out near idle. After finding out that nobody in town stocks TPS sensors for this car (???), I tracked down a good used one, tested it to confirm it works, and installed/calibrated it with high hopes that it would solve the problem.... NOPE! No change at all. The idle is still high and erratic.

I think I'm back to either a bad ecu, or a wiring problem (remember, I did an auto to manual swap and ecu swap)...

Can anybody post links or pinout diagrams for an automatic 88 crx dx and a manual 88/89 CRX dx manual? I have looked and haven't been able to find anything that differentiates between the two.... The only differences I know about are the backup light and neutral lockout, and that's all I changed when I did the swap......

[GasSavers_bobski]

As for the spring, I was just throwing ideas out there... If the spring was missing, I could see vibration and/or the throttle cam tapping on the end of it possibly causing inconsistent idle speeds.


You didn't accidently switch around the IACV and tandem control solenoid valve connectors, did you?


Wires that differ at the ECU:
- Lockup control solenoid
- Interlock control signal

Elsewhere:
- Shift indicator wiring
- Interlock control unit wiring and associated shifter and ignition switch solenoids
- Neutral / clutch safety switch wiring

The main wiring harness should be identical between manual and automatic DXs. It's the engine, dashboard and rear wiring harnesses that vary.

[101mpg]

I have a similar problem on my 89 DX (no swap). Doesn't always idle high, but has the hunting problem, and if I give it gas it's like I have a dead spot - then it will rev back to life wherever the accelerator position is. Checked and the TPS is fine.

I will be replacing my fuel pump and fuel relay. Timing belt is brand new, btw. I am wondering if it's a faulty O2 sensor as well. Bobski or anyone - know of a cheap place to get a new O2 sensor for an 88/89 DX auto? I'll be reporting my results.

BTW I have heard it can be the fuel relay - that's why I'm changing both. The fuel pump was about $40 online, too. Chances are you still have the 20+ year old fuel pump in yours - and the relays are known for going bad.

[GasSavers_Hal9000]

Thanks guys.

Bobski, by your description, it sounds like I don't need to worry about any wiring differences, right? Lockup Control solenoid wire is obviously disconnected at the trans since it's not there anymore, and by interlock control signal, I'm assuming you mean the wires at the shifter that I had to jumper together to disable the neutral lockout so I could start the car....

I'm going to throw my old Auto ECU back in when I get home and see if that changes things. (Fingers crossed!)

101mpg, I'll have to check my records, but I don't recall ever seeing the fuel pump/relay being replaced in the car's history. It's worth a try, but still, since the problem cropped up on the first drive after a trans/ecu swap, I'm of the opinion that all the things I'm checking at this point are long shots anyway.

Where's the relay at? If it's easily accessible, I can bench test it today.

[GasSavers_Hal9000]

Oh, and by the way, If you suspect your O2 sensor, you can usually remove it and burn it clean with a propane torch. Get the metal shroud around the sensor cherry red so it burns out any accumulated carbon, let it cool, then replace. If that is your problem, this should at least improve things. It's a trick that I learned from while having similar problems with the old mercedes I own (also first generation fuel injection).

If you use any anti sieze on the threads, be extra careful that you don't get it on the sensor. It can foul things up and give you bad readings.

[GasSavers_Hal9000]

Crap...

It's not the ECU, and it's not the O2 sensor.

Could it be a bad tach sensor or lead maybe?

I'm out of ideas at this point. I hate to give in and take it to a shop (even my cousin's shop). I've never had to do that before!

[mrmad]

I never saw in this thread that you did the correct procedure to set the idle. If you did, I apologize. That is to disconnect the EACV, set the idle with the air screw to ~650rpm unnder no load (no lights, A/C, etc). Shut the car off, connect the EACV, and reset the ECU by unplugging he hazard fuse from the main fuse box for 10 seconds, and then start the car and let it idle for a few minutes to let the ECU adjust the EACV on the idle. If you just adjust the air screw without resetting the ECU, it will get confused as it has a "memory" as to where the EACV valve is supposed to be from when the last time the ECU was reset.

The idle hunting like your description is what the ECU does when the idle is set too high. The ECU is programmed to shut the injectors off when the rpms are over 1100 rpm and the throttle is closed (like you were coasting in gear). If the idle is set too high, the rpms will go above 1100 rpm, and then drop back below it when the ECU cuts the injectors off. The idle basically bounces.

[GasSavers_bobski]

Originally Posted by mrmad

The idle hunting like your description is what the ECU does when the idle is set too high. The ECU is programmed to shut the injectors off when the rpms are over 1100 rpm and the throttle is closed (like you were coasting in gear). If the idle is set too high, the rpms will go above 1100 rpm, and then drop back below it when the ECU cuts the injectors off. The idle basically bounces.

Good point. I don't know why I didn't think of that... I've explained it to others in the past. Another characteristic of the idle-up/coast-down cycle is a relatively fast idle-down portion of the cycle. The idle-up speed depends on how high the idle has been set or how big the vacuum leak is.

[GasSavers_Hal9000]

I was actually about to post on another forum and ask what the procedure for setting the base idle is just to make sure that I had covered that base as well.

FWIW, I did slow the base idle down by a few rpm when I first started fighting this problem, but didn't follow the procedure you outlined.

So is the EACV the same as the Idle control valve? I'm assuming it is. Also, is this procedure for the DPFI system, MPFI system, or both (I've got bad advice from a lot of people who don't realize that depending on the model, '88-91 civic/crx's had two completely different fuel injection systems).

Would an incorrectly set idle also account for the exceptionally high idle when cold and not dropping to base idle nearly as fast as it should?