lrhtech

Hello All,

1997 Civic LX D16Y7 M/T, no engine mods

So I've been chasing idle problems for about a month now and here is where I'm at:

Original problem was high idle both cold and hot (~1400) and severe misfire for about 10 seconds after starting when cold. I cleaned the IACV and it didn't fix it, so I replaced it.

Here's my current situation:

No idle surge or hunting.

The idle was still high after I replaced the IACV so I went back to the manual.

There were no codes immediately after replacing the IACV, but it had thrown P0505 before so I started with that troubleshooting chart in the manual (pg 11-192). I fully warmed the engine and the idle was too high. It was above 550 rpm so I moved to chart "B" on the next page. I covered both ports one at a time (the text says "lower port" but the pic points to the upper port, hmmmm) and in both cases the idle speed dropped, so I went to adjust the base idle (pg 11-221). I left the IACV connected as per the instructions.

What I found was I could not lower the base idle speed below 850 rpm even after turning the base idle screw all the way clockwise until it stopped turning. Spec for my motor in the USA is 670 +/- 50 rpm. But I turned it as low as I could and moved on. I turned on the A/C per the book... the idle speed dropped to about 450 rpm. So, the IACV was not bumping up the idle speed. This took me to pg 11-204 to test the A/C signal. Everything tested ok.

So, here's the deal: If any load is turned on (A/C, headlights, rear defrost), the idle speed drops and does not come up. It can drop 600-900 rpm.

Disconnecting the IACV does nothing to the idle speed (but does throw a code immediately).

I noticed the IACV port in the intake was always sucking, even when the engine was warm with no load.

If I put my hand over the throttle body, the engine dies.

The PCV valve clicks when I pinch the hose.

I sprayed around with carb cleaner but did not find any idle speed change (vacuum leaks). I pinched every hose I could find at both ends with no idle speed change.

I plugged the old IACV in and it operated (actually kinda cool, the little rotary valve was moving so fast I couldn't see it, but I could feel it when I touched it).

Again, normal idle with no load is too high, a load does not bump up the idle, CEL is now on with P0505, and the old IACV does operate so I know it is getting some kind of signal from the ECU.

Any help is appreciated.

lrhtech

Former User

Make sure the throttle cable has some slack and then follow instructions below for the D16Y7. You need to use an accurate external tachometer.

lrhtech

Thanks!

Yep, it has slack. And, those are the idle speed adjustment procedures I used.

Also, on a related note, the throttle plate is closed all the way and I cleaned out both intake ports and Sea-Foamed the engine.

lrhtech

Former User

Did you use an accurate external tach to measure engine idle rpm for the procedure?

lrhtech

I did, I was reading it off of the screen of my code reader in monitor mode.

lrhtech

Former User

Is the ignition timing set to spec?

lrhtech

I'll check it, but I did check it when I bought the car this past summer and don't suspect that the distributor has come loose and turned, so it is likely to be accurate.

Former User

Test the TPS and ECT sensor.

lrhtech

What do you think about the IACV letting air through even when the engine is warmed up and there is no load? This is when the base idle screw was not fully closed (idle in the 1400 range)? Seems like it should only let air through when it needs to bump up the idle due to load or a cold engine.

lrhtech

The scan tool reported the TPS was at 9.8% at idle, which is in spec (about 10%). I'll check on the ECT sensor.

Former User

What was temp did the scan tool read for the fully warmed engine?

lrhtech

The ECT sounds promising, if it never closes the IACV may think the engine is still cold and be in a perpetual state of trying to bump up the rpm... which would explain a lot.

Just wondering if a bad ECT would show up in other problems, which I don't have.

lrhtech

I'm really sure it said 194 degrees, but I didn't make note of it. I do remember looking at it and it didn't raise a flag in my mind.

lrhtech

OK, so here's what I found:

TIming is good.

The ECT in the thermostat is good (it just turns on the fan anyway).

The ECT under the distributor is good. Engine temp 195 degrees.

That's all for now.

lrhtech

OK, so I am continuing this saga of nailing down the P0505 IACV system problem.


I decided to check all the inputs that the ECM gets. I started with the clutch switch signal.


Funny thing is, the 1996-2000 Civic Service Manual does not have a page for testing the CLSW that applies to my car. The only car listed for the CLSW is "D16Y5 engine with M/T" (page 11-218). As this was the only CLSW testing procedure, I figured I better try to use it. But, alas, my 1997 Civic LX D16Y7 M/T does not have a wire in position C29 as required to do the troubleshooting procedure. So, no-go on testing the voltage signal at the ECM.


Another funny thing, I figured I'd go ahead and test the switch so I disconnected the the 2P connector from the CLSW and checked for continuity. I discovered it is backwards from what the manual says it should be. I have continuity when the pedal is in the resting position, and the CLSW is open when the pedal is depressed. Hmmmmm. Not convinced the switch is bad though, maybe it is a typo in the manual... it has been known to happen before. I'll try adjusting the switch, maybe.


Please note I am not referring to the clutch inter-lock switch. The car will still start if I push the clutch pedal all the way down.


lrhtech

lrhtech

OK, so here is where I am at: I find that the ECM is to blame. Here's why:


1997 Civic 4dr LX D16Y7 5MT CA-model


I checked all of the signal inputs to the ECM, as follows:


Clutch Switch (pg 11-218): As described in my previous post, just doing the troubleshooting gave me trouble. There is no page in the book for my car, the closest is "D16Y5 engine with M/T". This issue became blatantly obvious when I tried to do step 1 in the TS chart and saw that I have no wire in spot C29. So, I moved on, and checked the switch itself. It works backwards of how the book says it should work (continuity with clutch pedal at rest, no continuity with pedal depressed). But, I think this is a typo in the book... My cruise control works (normally it wouldn't if the clutch switch was bad), and I don't see the clutch switch causing any problems.


Power Steering Pressure (pg 11-212): "Is there less than 1.0v?" Yes, .001v. "Is there battery voltage?" Yes, 13.7v. PSP is good.


Alternator Signal (pg 11-208): "Is there approx. 5v?" Yes, 5v. "Does the voltage decrease...?" yes, from 3.8v to 2.8v. "Alternator FR signal is OK"


Starter Switch Signal (pg 11-202): "Is there battery voltage when cranking?" Wellllllllll, pretty much... 9.8v at ECM connector when cranking, when the battery voltage at the battery is 11.1v. But its close enough, I think.


Brake Switch Signal (pg 11-210): "Are the brake lights on?" No. "Do the brake lights come on?" Yes. "Is there battery voltage?" Yes. "Brake switch signal is ok."


Air Conditioning Signal (pg 11-204): "IS there approx. 5v?" Yes, 4.7v. "Is there a clicking sound from the A/C compressor clutch?" Yes. "Does the A/C operate?" Yes. "A/C signal is ok."


The following are picked and choosed tests from the TS procedures, because the only code the CEL ever shows is O0505. So you can't really TS a problem that isn't happening and not throwing a code. The service manual acknowledges this and just gives instructions to check a few connections. But I thought it might be useful to check a few actual parts.


Throttle Position Sensor (pg 11-136): "Is there approx. 10% when throttle is fully closed and approx. 90% when the throttle is full open?" Yes, 9.8% and 89.8%.


Electrical Load Detector (pg 11-181): "Is there battery voltage?" Yes, 12.8v. "Is there continuity?" Yes. Is there continuity?" Yes. "Is there continuity?" Well, no actually... there was a weak connection, but not full continuity. I cleaned the connection at the 3P connector under the ELD and now there is continuity, so the answer became Yes and I moved on. (the idle issues were not fixed by this.) "Does the voltage drop?" Yes, 3.6v to 2.8v.


I then did the test for P1509 (even though that never comes up) and it gets more interesting here. Again, unfortunately, I'm not sure pg 11-198 applies to my car, because it says it is for "96-98 A/T and D16Y7 engine". Depending on how you read this, it is either for 96-98's with A/T AND a D16Y7 engine, OR its for 96-98's with A/T and all D16Y7 engines.


IAC Valve (pg 11-198): "Is there more than 1v?" No, .01v on both. "Is there battery voltage?" Yes, 12.8v on both. "Is there 16-28 ohms?" Yes, 22 ohms on each. "Replace ECM".


I think replacing the ECM is where I'm at. I've replaced the IACV and searched for vacuum leaks and found none. I took the throttle body off yesterday and saw nothing out of order.


I tried adjusting the idle again. I can close the idle adjustment screw all the way and the engine still idles about 750rpm. When I turn on the lights/rear defogger or the A/C, the idle drops significantly (Down to about 600 rpm from 1100 rpm where I have it set now so it doesn't die.


It really seems like the ECM is telling the IACV to boost the idle when it shouldn't, which is why the engine idles at ~750 rpm even with the idle screw totally closed, and why the rpm's don't come up when there is a load... the IACV is already at max boost and can't boost it anymore.


Long post, I know, but I really want to get this figured out.


Thoughts?


lrhtech

Former User

If you reset the ECU, does P0505 return? If so, does an idle problem accompany the code? If so, describe.

lrhtech

Yep, P0505 will return, it usually takes about 40 miles of driving and the light comes on. The car then runs all-around-crappy due to "limp mode" until I reset the ECU.


The idle problem exists whether the CEL is on or not (or pending or not.)


The idle problem is that the idle drops significantly when a load is placed on the engine. Both electrical (headlights/rear defogger/cooling fan) and physical loads (A/C compressor) drag down the idle. Also, there is a few seconds of misfiring immediately after starting the engine when cold.


I have the base idle set high (1100 rpm) right now so that the car is drivable. when turning on the A/C, the idle drops to 630 rpm. (If I set it to spec at 750+/-50, the idle drops so low under load (about 400rpm) that the A/C compressor starts disengaging/engaging very rapidly as the ECU tries to keep it from stalling... can't have that!).


lrhtecth

Former User

Why do you think the ECU goes into limp mode?

When you unplug the IACV, does the idle speed drop? If so,

1) Adjust the idle speed correctly as per service manual instructions. See FAQs sticky.

2) Test the TPS and ECT sensor.

lrhtech

I think its going into limp mode because of the code it is throwing (there are no codes besides P0505... ECU has detected a problem in the IACV system).


OK, but I checked those two items and they were good... Honda calls for "about 10% at closed throttle and 90% at WOT" for the TPS. My cars numbers are 9.8% and 89.8%. My two ECT's were good, the one at the thermostat housing turns on the fan like it should and the other one under the distributor is reporting accurate temps. I can watch the temp increase as the engine warms up, see the fan come on at 205, watch the temp go down as the fan cools the engine, etc.


So I'm still at a loss. :-(


lrhtech

R.Bush Mechanic

no evidence of blow back (carbon built up) anywhere on the intake manifold? If not i would look into cleaning the throttle plate, if you already did that then ECT or your car may have a aftermarket security system.

Former User

P0505 would not put the ECU into limp mode.

Voltage test the TPS and Ohm test the ECT sensor.

The fan switch on the thermostat housing is not relevant to P0505.

Do the IACV unplug test, and adjust idle speed if engine rpm drop.

Also clean the TB port leading to IACV.

tony_2018

confirm tps voltage

lrhtech

Thanks guys, gonna get some significant rain this week but I'll check it out as soon as it clears up.


"P0505 would not put the ECU into limp mode."


Except that it does. Here's the deal:


CEL off, no code pending: Car drives fine
CEL off, P0505 pending: Car drives fine
CEL on, code P0505 stored: Car instantly runs like crap, very jerky when driving, feels like I'm kicking the accelerator from closed to WOT when I'm trying to drive normal.
Clear the code: Car runs fine again instantly.


lrhtech

Former User

Define limp mode. The actual definition is very specific.

Running poorly does necessarily equal limp mode.

Also be aware that your previous TPS and ECT sensor troubleshooting are meaningless if done when the problem is not occurring.