chris00tt

I have a 94 Civic DX coupe that now has a D15B8 motor as the old motor had gone bad due to poor maintenance by previous owner. The D15B7 throttle body and intake manifold were swapped over to the D15B8 motor and a new water pump and timing belt was done, along with new plugs, wires, cap, rotor. During installation of the motor, the TPS sensor got cracked. I bought one locally that came off a B20 I believe. After all was set and done, I went to make some adjustments, but cannot get the idle to stop surging. Here are my issues:

1. I tried adjusting the TPS with the car off, but the ignition turned on. I was told to set the TPS voltage at .45V in this state, however, I was unable to do so. The voltage reading was 4.94V no matter where I rotated the TPS. I hooked up voltage across the yellow TPS wire and ground.

2. I tried setting ignition timing, but I cannot get the white TDC mark to line up with the groove in the timing cover. The distributor is maxed out completely in one direction and I am still about an inch away from the groove.

3. The D15B8 motor did not have a "Y" in the water line coming out of the water pump like the D15B7. As a result, I had to block off the water lines running into the Idle Air Control valve (IAC) as well as the lines running to the throttle body. If this design is at all similar to the one Mitsubishi used on their 1g DSM's (Fast Idle Air Valve, or FIAV, for cold starts) then I know this shouldn't cause any issues.

Upon doing some reading and thinking about the situation, I rechecked cam timing and all marks were dead on. The white TDC mark lined up with the groove in the timing case and at that point the cam gear had "UP" facing upwards and the two horizontal marks were parellel to the flat plane of the cylinder head.

This is really frustrating as nothing seems obvious, besides perhaps a bad TPS. I did try to unplug the IAC and adjust the idle screw, but as soon as I plugged the IAC back in, the idle would continue to surge. Any help is much appreciated as I'm not very familiar with Honda. Thanks in advance!

lightcrx

check for vacuum leaks, if you cant get the timing mark on then the timing is off.. redo the timing and try again

chris00tt

I will check for vacuum leaks, but I know all timing marks align properly so cam timing is set correctly.

Another thing, is there any difference between distributors from the D15B7 to D15B8? I am using the B7 distributor on the B8.

RockinthEFhatch

If you look in the throttle body cover the lower hole with your thumb and you should feel a vaccum. With your thumb over the hole, sealing it, the idle should go back to normal. If this is the case its your Fast Idler Thermo Valve is bad and will probably need to be replaced. If there is no suction from the lower hole the FITV is fine and you need to figure out what else it could be. This happened to me so I just solved the problem by buying a Spoon Sports TB

This is the FITV that will need to be replaced.

chris00tt

Thanks for the post RockinthEFhatch. I have another question about this FITV. The D15B8 motor had a water pipe that did not have a provision for a coolant line running up into the IATV. As a result, I blocked off coolant flowing through the IATV and FITV. Will this cause a problem aside from a vaccum leak? I will check for the vac leak and see if that gets me anywhere.

chris00tt

Just got back in from looking at the car again, and noticed that the throttle body does not have a lower vac hose that you suggested. In fact, the only vac lines I can find are the ones running off the FPR, the one running to the brake booster, and ones for the evap system. The throttle body and intake manifold are from the D15B7 as the D15B8 throttle body and intake manifold were much smaller and did not fit the factory air intake tube.

I took off the IACV and replaced the old o-ring type gasket with some silicon. I've noticed that if this is unplugged, the car idles great and sounds perfect. Once I reconnect it, it begins to surge and the engine speed raises. I will try a known working IACV and see if that fixes the issue.

I'm still puzzled as to why I cannot get ignition timing back into spec. The distributor is bottomed out, but the timing mark is still advanced beyond the mark. As stated before, I rechecked cam timing and it is dead on. With the white mark on the crank pulley at the TDC groove on the timing case, the cam pulley has "UP" facing upwards and the two side tick marks are parallel with the cylinder head.

lightcrx

put sumin in the spark plug hole(long stick or sumin) and make sure the pully is right. when the object stops and going up thats tdc ;] make sure the pully is right, some one could have change the pully... never know

Mr. Nop from C*H

chris00tt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by moops vs moors &raquo;</TD></TR><TR><TD CLASS="quote">
air in the coolant system can also cause similar problems, might wanna try bleeding the coolant.
</TD></TR></TABLE>

This would only be true IF the FITV was hooked up correct? The water pipe on the D15B8 did not have a "Y" built in so I could not run the coolant hoses to the IACV and then to the throttle body.

I do appreciate all the suggestions and I will hopefully get to the bottom of this sooner than later. I will keep the post updated with my findings. Thanks guys!

89 civic si

your fitv must have coolant going into it must the idle will never be right

chris00tt

I finally solved the problem today. I found some information on the spring loaded plunger inside the FITV coming loose over time and causing issues. I took the throttle body off and apart today to tighten this up. It was fairly loose and I got around 4 turns or so IIRC. I then reinstalled the throttle body and let the car warm up. Wouldn't you know, no more idle surge!

If you suspect your FITV has gone bad, try taking the throttle body off and locating the two 8mm bolts that hold a cover plate on the FITV (on the side of the throttle body that faces the firewall when installed in the car). Inside you will see a yellow grooved plastic washer with a black retractable plunger through the center. The yellow grooved plastic washer has detents on both sides so that you can use a flatblade screwdriver to tighten it down. This took about 20 minutes total and instantly cured the problem.

Also, for those who have been following this post, the ignition timing problem I had was simply an error on my part. I was trying to adjust the timing cover mark to the white tick mark instead of the red tick mark. This was not made clear in the Haynes manual I have, at least not my edition.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 89 civic si &raquo;</TD></TR><TR><TD CLASS="quote">your fitv must have coolant going into it must the idle will never be right</TD></TR></TABLE>

I just disproved this about 30 minutes ago I have the FITV bypassed so that no coolant flows through it. I wouldn't do this normally, but the D15B8 I installed does not have a provision for an extra coolant line running up the IATV like the D15B7 did. The car idles smooth and steady without any issues, especially after adjusting the valve lash earlier.

Thanks for all the suggestions over the past few days and I do appreciate all your input!

Iron_Forrix

i hate cold mornings as so does my car, its having starting troubles and the cold only makes it worse. When starting my car on a cold start after its been sitting aorund for a few hours (or all night) the idle is real high (2500-3000rpm) then it pulses/fluctates each second up and down from around 1000 back to 3000. Once i let it do this for a while the high end of the idle gets lower and lower and eventually the idle is just fine, down to a normal 500-750ish. Only works right when its wamred up

The colder the engine, the harder it is to get the car to start, which is harder to keep it alive cause it fluctates so bad on freezing mornings it shuts off.

A buddy of mine told me to take apart the sall peice behind the throttle body with the plug and 2 hoses (in my 91 crx hf) did it but didnt change anything. Hes unavailable and i sure as hell dont want to shop this one. Winter is upon me help!

chris00tt

I would check your battery. Winter is notorious for making weak/old batteries die out. When was the last time this was replaced? Have it checked if you are uncertain, as this could be the cause of the hard starts.

In addition, check the Fast Idle Thermo Valve to make sure it is tight. I took the cover off of this and tightened it up and my surge disappeared. Look at the picture posted above and you will see the FITV I'm talking about. On the side facing the firewall, which you cannot see in the pic, is the cover plate that needs to be removed (2 8mm bolts). Tighten up the valve inside and see how this turns out for you. I hope this helps.