I just installed my recently rebuilt 13bt engine into my car and found that upon starting, the engine would just rev by itself without me touching the accelerator at all. The tacho showed 0 revs the whole time, so after fooling around with some vacuum lines (the 4 lines behind secondary fuel rail), the tacho started working again on the next startup... i dont understand how that affects it..

with that working, the tacho shows the engine rise to 5000 rpms at which point i turn off the engine to prevent damage..

ive checked for any massive vacuum leaks, checked all plugs, checked for spark, checked bac valve lines and plug, unpluged tps (wouldnt start), played with idle screws, checked ecu harness connections..

ive taken it to the shop i had the engine rebuilt at, hopefully they'll get back to me tomorrow.. but in the mean time, any ideas?


rx7 s5 13bt, removed acv, sap and air pump (block off plates), stock ecu

 

I have no idea about your problem there.. Just wanted to say I like your avitar

 

Try loosening your throttle cable.

 

nope, apparantly throttle cable is ok...

any other ideas?

would 3 month old fuel cause this?

 

Does it sound like 5000RPM?

 

well, there is the auto-warm-up feature, but it only takes the engine up to 3100-3200

5K seems a lot. Maybe your thermowax is out of whack ?

 

This same exact thing happened to me, right after i did the tb mod and some other mods. I started the engine and it really slowly just started to rev higher and higher. After like 5 or so seconds it was up to like 5 or 6 grand and not slowing down. I just went under the hood and pulled on all of the cables going to the throttle body and moved all the butterfly plates and made sure they weren't stuck in place. I restarted and it was fine. You might have something jammed in there.
Craig

 

ok, the shop thinks it may be the gasket on the lower intake manifold.. if this was leaking, could it cause such a high idle??
even if it is leaking, wouldnt the idle only slightly increase?

oh, they want to pull the engine to change the gasket and those little O-rings, "because its quicker that way". Is this true? or does it sound like a last ditch effort to find the problem?

thanks fasthack, i think ill go get the car and try what you have.

 

mine'll rev to about 4k if I start it in "N" before it drops down to 3k... it's only surposed to go to 3k though, never bothered to look what it was, I just start it in gear to bypass the cold start. cause even 3k is too high for a start up I think.

 

yeah u ever try putting it in gear and start it
i do that all the time since the auto reving to 3k is kinda loud

 

Does your air bypass valve on the upper right hand side of the engine have two hoses connected to it???? Take the plug off your AIR BYPASS VALVE and start the car. Does it idle lower??????AIR BYPASS VALVE is located inboard of the where your bac was, and is inches from the intercooler. Has one hose going to the intercooler. Also the AIR SUPPLY VALVE is located on the back of the throttle body and should have one hose going to the rear of the intercoooler. Is it on????
The AIR BYPASS VALVE is the the component that causes your car to rev to 3000 rpm at start up for 17 seconds. If you disconnect it obviously you disable it and eliminate it as a source of high idle.
Why did you take the BAC off??? Its your best friend.

 

nono i still have my BAC valve!

this is a series 5 engine, i dont think it has the air supply valve on the back of the throttle body.. (i dont see it)

the air bypass valve. is that also reffered to as the blow off valve? if so, it is now atmosphere vented with a 1-way check valve on the end (was working before the rebuild, not touched either, (yes i blocked the leftover air box hole)) will it still cause the 3000rpm startup even though it cant suck air back through?

 

Yes. I should stop here. I don't have a series five. The AIR BYPASS SOLENOID VALVE on a series four is located maybe a inch inboard and an inch aft of the BAC. The rear hose on the bac on a series four goes to the air bypass solenoid valve. The air bypass solenoid valve on a series four has another hose that goes to the intercooler. And now for TRUE CONFESSIONS. In the original post I left off the SOLENOID word b/t bypass and valve. Words indeed do have meaning. On the turbo you have a air bypass solenoid valve as described above and a air bypass valve. Two seperate things. The air bypass valve is what I guess is what you refered to as a blow off valve used to relieve pressure back into the inlet duct during decelleration. So yours is open to atmosphere? Hmmm. Makes you want to have someone put their finger over it while you startt the car to see if its sucking air. What do you think???? Yes my first post was misleading because I left the word SOLENOID out of the phrase. I'll go sit in the corner now with my dunce hat. Try that part about putting your hand over the air bypass(blow off)valve during the startup.

 

Read this thread and the reply by DCAMCO https://www.rx7club.com/forum/showth...ght=inlet+duct I think it relates to your problem. You did mention the bypass was vented to atmosphere with a one way check valve, but maybe something can be gained by reading the above thread.

 

hailers, what happens when you disconnect the water thermo sensor on the battery side of the engine block? (just above the oil pressure sensor) will this cause the fast warmup to run continuosly?

 

No, thats just a temp sensor for the water temp gauge. There is a switch on the bottom left side of the radiator on my 87 that you can take one or both bullets off, and will disable the 17 second warm up, but when that is done you disable a function of the relief solenoid. But your car is series five and from what I read, it does not have the sw at the bottom of the radiator. I figure your car has a air bypass solenoid valve somewhere . Its above and aft of the bac on a series four turbo.
I just looked at the HAYNES manual (not sure if I can trust it) and it shows a 89 schematic and they call the AIR BYPASS SOLENOID VALCE something else. They did not like calling Bob, Bob so they thought they'd call him Sue. humor. They call it SOLENOID VALVE(accelerated warm up system) and it is where I said, just above and aft of the bac. Try taking its plug off. The 17 sec run up to 3000 should cease.
Did yu ever try putting your finger over that air bypass valve down on the inlet duct that you said was sitting out in mid air with a check valve on the end?????

 

yes, i did try covering the Air Bypass Valve with check valve. No air is being sucked through or blown out.

I cant see the solenoid valve! Would it be a part of the ACV? here is a couple of pics in the general BAC valve region..







hard to see anything in them, but there is definitly no air bypass solenoid valve

 

I don't see it either. They must use a different method on your model. Sorry I wasted your time. I should have dropped out when I realized you had a series five. No air supply valve on the back of it either.Just like you said. I'm sure you looked at the throttle plates to make sure they are closing all they way(assuming the intake is off like in the picture). Sorry, no idea.

 

Damnit Ill have to wait for the series 5 manual to be posted online.

 

isn't there a adjustment for the fast idle cam? when a friend of mine asked me to look at his car because his car was idleing at 1.5k rpm when fully warmed up, i fornd a number of vacume leaks. after i changed some hoses and fixed some cracks when we started the car the car reved up to 5k rpm. what i think happened was the previous owner couldn't find or see the leaks i found so he played with the idle adjustments a little. so after i fixed them the car idled very high. (am i making sense? i just read this reply and im confusing myself)

 

flyingoufer in the above post has a good idea. I suggested the same in a couple of posts above about checking the throttle plates to see if they are all the way closed. I think you have the throttle body off because of the pictures. Right. Should be easy to check with the throttle body off as in the picture.

 

yes, it was removed and i checked the plates visually by removing the upper manifold from the actual throttle body. The plates seal right, flush against the openings.. Also, I did not change any settings before it was removed when it was working right.

The wire that connects to the water temp sensor on the engine block has broken off, so i'm hoping it isnt affecting the problem. Does the air hose on the BAC valve connect directly to the verticle air pipe (from turbo to intercooler) OR does it connect to the small air pipe hole on the air box (housing the air filter). I need to know this as my ACV and air pump is removed.

 

Connects to the pipe from the turbo to the intercooler. The one on the filter went to the airpump.
EDIT: Any chance that the blockoff plate for the removed acv is leaking?

 

While tearing the damn thing down yet AGAIN, I was checking the vacuum lines, and i found the largish type vacuum line that connects to the Wastegate Valve Actuator to be split lengthways! Would this be enough to cause the problem!? would my wastegate be working at all?