When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Did not know a better spot to put this so i tossed it into the general FD forum, mods feel free to move it to a technical area if thats for the best but I did not see one when i scanned for it.
I have a mostly stock 95 FD, its got a downpipe and highflow cat and other than that the engine is as it came from the factory. Since I have owned the car it has had a high 1200-1500 rpm idle, a little stumble, a little engine shake and a touch of backfire when you let off after getting into it. Low speed crusing with the AC on can also cause bucking from time to time. Other than that, the car makes good power like it should, its got a good 10-8-10 boost pattern and at speed I have redone all of the vacuum nest about 4 years ago, and it did not fix the issue. Curiously, when the car is really hot, like traffic for hours or things are just right, it on rare occasional idles correctly, stumble gone, smooth 900 rpm.
Tore the thing apart today hoping to fix it once and for all,
Checked the Wax Valve and saw it was working correctly, after getting hot it extended and pushed the pin away (sitting at the C setting) so that was not my prob (replaced it anyways because i had the part)
Verified the air adjusting screw was totally in and closed, so no lower RPM possible there, rpm did increase when opening further
Verified the throttle adjusting screw was just contacting the throttle at full close and was not increasing RPM
Strangely I noticed my RPM did not drop when I hooked up Ground to TEN on the diagnostic port... not sure what that means
Got my Throttle Position Sensor jumper and checked adjustment, they seem dead on.
Top reading was 0.96 closed - 4.98 full open
Bottom reading was 0.43 closed - 4.36 full open
Checked the Idle Air control valve it moves with a little 12v jumper and has 11.9 ohms resistance, in range
Checked the Accelerated Warm up Solenoid and it moves with a little 12V but it has 12.5 ohms resistance putting it out of range for the factory manual
Could it be that easy? Anything else I should check before buying one of these, they are 200$ and I'm pretty excited to find something after hauling out my extension manifold, Any other ideas or thoughts? I would love to have this issue solved.
Some photos of the fun included
Thanks all.
Last edited by wireclimer; 05-17-20 at 09:49 AM.
Reason: wrong photo file type
You most likely have a vacuum leak between the throttle body and the engine. With the engine warmed up, the throttle plates will be fully closed and the ISC bypasses air around the plates to set the idle speed. If some other air gets in, that will raise the idle.
Any way that air can get in will cause this - not just a vacuum hose, but a bad gasket, injector seals, etc.
Best way I've found to spot vacuum leaks is to get a can of starting fluid. Slowly spray it around the intake manifold, if the engine sucks the starting fluid in the engine will rev up/smooth out for a sec. That can help narrow down where the problem is.
Also your pictures are HEIC files, they don't natively show in the Forum software. You may want to re-upload them as JPG files to make it easier to view.
Ahh, I thought HEIC were listed as supported when I looked, surprised me as well. Ill change em, just shots of throttle bodies and rats nests.
So you would advocate some gasket replacement and tightening everything up then spray her down with the ether to see if i can get it to surge, I did not do that before i took it apart... Would you think that is being more likely of an issue than the AWS on a car that otherwise runs well? Happy to try it.
That would bring up some intake manifold areas as well into the mix. yay.
I'm hoping it's something up high in the system that's easy to get to. It COULD be something like the AWS stuck open as well, that's possible.
Since you have a '95 I doubt you have the old paper lower intake manifold to engine gasket. Those blew out and leaked all the time. I think they changed to metal by '95.
All the intake manifold gaskets - ISC, AWS, TB to UIM, UIM-LIM, and LIM-engine should be metal. If any of them are paper they could be compromised.
Just a note~ you stated the air adjustment screw is turned totally in and the throttle body adjustment screw is just making contact. I would generally check that the secondary butterfly stop isn’t out of adjustment. But I have to agree with dale, it’s a vacuum leak for sure. Tho I’ve never been very good with the starter fluid trick, I would perform the smoke test on it. I seem to remember a member having an issue like yours which turned out to be the donut seals around the injectors. Just two penny’s for ya.
Thanks,
I will check the secondary butterflies but i do think they were OK. All of the gaskets i have ran into are metal, i did new o rings when i had the injectors out a few years back for bench flow check, and all the gaskets I have ran across so far are metal, I have never seen the intake manifold gasket as i have never taken it off. Really hope I dont have to...
Dont know why excess air from a vacuum leak never occurred to me, valuable thought from you guys, thanks.
I am familiar with doing the start fluid method, less so with the smoke method but the interwebs seems to explain it pretty well. How would you even see it coming from something under the extension manifold? goodness.I will drop the money on some new gaskets and the new AWS and ill have a put it back together and check it over and over party next weekend after the parts arrive. Would be great to have this sorted but it doesnt make sense to not buy all the stuff and find out its one or the other for 2 weeks over 300$ Buy all the things.
Guess I am starting to see the value in blocking off all that crap and running a stand alone. Few more years and I guess we wont be able to find all of the parts to keep a car running stock anyhow.
One other trick that can sometimes help find vacuum leaks is run the engine with the intake elbow removed. You'll hear a strong hissing sound where the air is being sucked quickly across the mostly-closed throttle plate and through the small holes for the idle valve and the bypass screw. Then use something flat and sturdy (piece of metal, strong plastic, strong cardboard, etc) to block the throttle body which should be supplying all the air for the engine to run. It might also be possible to block using a sturdy shop rag, but be careful to avoid pieces getting shredded and sucked into the engine. The engine should stall when you block all the airflow and if there are vacuum leaks somewhere else in the intake manifold you might hear them. With a large enough leak, the engine might keep running at a low RPM.
For what it's worth, I've been running my car's mostly-stock engine with a standalone and the IAC only (thermowax valve removed, AWS blocked off) for years and years now. It behaves very well, can idle higher than needed (1800+ RPM) when cold and as low as 700 when warm. I think I adjusted the idle bypass screw so the IAC is somewhere in the range of 20%-40% duty cycle at a normal 900 RPM warm idle.
Also, I would try disconnecting the air hose that supplies the AWS and blocking it off to confirm that solves your leak rather than buying a new one. It's a medium-sized line going to the intake elbow. I would be surprised if 12.5 ohms resistance means the solenoid is leaking air, but blocking the supply to the AWS should be easy to test. Even just blocking it with your hand should make it easy to feel if there's suction or not. Be careful of the plastic intake elbow, it might be brittle.
So it will be a few days before i get some parts, I decided to go grab gaskets and the AWS anyways, If I dedicate the next weekend to this party I would rather have the things I need to start troubleshooting all ready, very good ideas on blocking off the throttle plate etc to check for leaks.
One question I had, I checked the double throttle butterflies and the actuator works fine, not sure it works with the car on since it is still dissembled for now (intake extension and TB are off) but the secondary butterflies, the ones on the Intake extension do not fully close, the adjustment screw is set a bit shy of full close. Should they go to full close, and should I adjust the stop screw and make that change?
I know that wont be my problem most likely and I hate changing multiple variables while solving a problem (not more than I hate taking off and putting back on the intake manifold extension however) so I wanted to see what the thought was on that.
On a manual transmission car the secondary throttle plates just choke the engine down when it's stone cold. I think around 50-60 deg. C they open up and stay open. There may be something in the shop manual about how closed they should be but it really shouldn't make any difference. They are only there to choke down the engine so you don't have full power when the car is cold. They won't change anything about your idle or how the car generally runs.
Automatic transmission cars do something with them in certain circumstances, I don't remember all the details, I don't know the auto trans stuff that well.
I looked around the factory manual in section F and did not find adjustment values for the secondary butterflies but ill be good then with they can be open a crack and cant wait to dig into this thing this weekend (hopefully)
Armed with a pile of gaskets bought so I would have the right part I of course found out none of them were my problem and now I have a lot of gaskets, you know, for the future ( -;
After a lot of help to get to the logic that my fast and rough idle must be due to excess air getting past my throttle body somehow (and confirming I had no issues with the throttle plates or idle screw or wax pellet or throttle body sensor) whew! I was able to get to a place where I knew I needed to find a leak in the intake side of the party.
I used the suggestion on smoking the intake track suggested by you guys, I was worried I would have to buy this 400$ smoke maker from Amazon and then a fellow car guy found a video about using cheap cigars, I didn't know how to do it the easy cheap way until I saw the video,
Its brilliant, and after my own visit to harbor freight after I concluded some business regarding jackstands I bought my very own 6.90$ transfer pump and a pack of swisher sweets on the way home. Tonight the help stopped by and provided hands, tools, beer, we lit the cigars and pumped cigar smoke into the upper extension manifold nipple hoping for something to happen and after a bit there was a curious puff faintly coming from the front area somewhere under the air pump where a flash light could not quite identify.
Started part by part disassembly, pulled off the turbo to intercooler pipe, relieved it wasn't coming from under the UIM where i would never know what was going on, BOV's off, Airbox out, could see it was coming from somewhere under the coolant neck, upper coolant hose off, and then Bam, The intake manifold has a missing section and has blown out. leaking boost, and gas on throttle and sucking air the rest of the time. I finally know whats up with the car.
Now I just have to take the whole damn thing apart to replace that gasket... and I promised myself that would be the last time I took the rats next out. crap. But I am really excited I know whats wrong and where to go next! So Thanks!
I guess I should of linked that homemade smoke machine when I suggested you do that procedure. That’s exactly what and how I do it. I’m glad you found something. Chasing those leaks down can be a time consuming process.
I guess I should of linked that homemade smoke machine when I suggested you do that procedure. That’s exactly what and how I do it. I’m glad you found something. Chasing those leaks down can be a time consuming process.
Not a problem, cant spell out everything for everyone and after some looking I was able to figure it out. Its nice to struggle a bit and then get it understood. I appreciate the method suggestion still, I can not figure how I would have had success with starting fluid, no way I would have gotten it down into those areas with the engine running and not blowing up my garage/car (-=!
Do you have a picture of where the leak is? Is it the lower intake manifold to engine gasket??
Glad you're making progress!
Dale
It does look to be the bottom of the lower intake manifold connecting to the block, check the short MOV movie file, I hope it plays??? you can see "in person" there is a gap and its missing a chunk where the leak is, I wanted to ask, if its an all metal gasket, does this mean someone had that off and was messing around with stuff? or do they really blow out and fail like that.
It does bring a bunch of symptoms into light... Ordered up a new gasket and some oil lines since those looked crappy last time I was that far in. Not excited to take it all apart, but also excited to take it all apart and get it right again (-=
Guess that means the front rotor has not been making the power it should ever since I have owned it. Terrific.
Last edited by wireclimer; 05-28-20 at 11:21 AM.
Reason: bad grammar (-=
Just watched the video file, that makes more sense now.
The original LIM gasket was paper and they were a common problem to blow out. The new one is multi layer steel and pretty much NEVER has a problem.
The sucky thing is you will need to pull the turbos to get in there. But, you don't have to pull the rat's next - the secondary fuel rail is bolted to the UIM and a few vacuum lines, once those are undone you can remove it, just leave the rat's nest in place.
You do have to make TOTALLY sure that you have all the old gasket off both surfaces. A tiny lump of old material can cause the new gasket not to sit flush and you'll be back at square 1.
It will be a whole new car once you are done, though!
I would read up on what all you should have on hand to pull and re-install the turbos. It's not terrible but if you break studs/siezed nuts that gets to be less fun quickly. Make SURE to soak everything in PB Blaster to give every chance of success.
Personally I'd get everything off one day then put everything back together the next day. Take your time and be prepared to walk away and order parts if necessary.
I ordered the LIM gasket already, but it looks like I will need more for the turbo's then. I think I'll do the disassembly and then an inventory to see what else I need to replace then do a last order. Good think Atkins and Mazdatrix are still shipping.
good council from you guys, deep breath and Zen and the art of Rx-7 Maintenance.
Quick question, does anyone still sell the turbo heat shields? are they affordable? is there a budget solution that's decent? I don't have good hopes on mine being reinstall worthy.
Quick question, does anyone still sell the turbo heat shields? are they affordable? is there a budget solution that's decent? I don't have good hopes on mine being reinstall worthy.
I was able to find a used set for $70 a year or two back. I painted them and they look fine now. I also bought a brand new manifold heat shield from Mazda for $50, but it had to come from Japan. I was able to wait because the engine was being rebuilt but it took 10 weeks, without covid.
The heat shields pretty much all look ratty, I've seen low mileage ones that didn't look great. They are under a LOT of abuse with the high temps they see.
Make sure to soak the 10mm bolts with PB Blaster ahead of time, those bolts love to snap off.
I wouldn't get too excited with how the heat shields look. They aren't visible when the turbos are installed. If you try high-temp paint it will most likely burn off and you still won't be able to see it.
Well it took a few nights of work, and a lot of being under the car to get it all apart but finally was able to get the trubos off and then the LIM, sure enough there was a big hunk missing out of the front rotors intake on a blue paper gasket. Took almost an hour to get the gasket material off, and found some nice dirt and a bunch of nuts from whomever did less than fastidious work on the car in the past... Cleaned it all up used a razor until the gasket surface was clean and reinstalled the LIM now on to the turbos as soon as the gaskets arrive.
Im pretty excited i got it apart without anything breaking and this is certainly as far into my car as I have ever been. Pretty proud, and Ill be pretty happy if it runs well and this is all fixed when its back together.
Brings up a thought, ive got the idle screw all the way in, no air flow and a new wax pellet installed too. Should I expect to need to open my idle speed screw a couple turns when I get it all back together?
just separated LIM from the block, there's the problem right there All surfaces cleaned up and ready to mount, had to razor, clean solvent wipe and toothbrush and vacuum to get it ready to go. Old paper gasket has the same consistency as rock glued to metal... Ready for the LIM to go back on Moment of much happiness with the LIM off finally
It changed during the production run. It's uncommon to see paper gaskets now, due to either the engine being replaced or the gasket blowing out and leaking.
I think by the '94s they were updated, but not sure of the exact point.
It should start with the air screw open a half turn, but you should follow the service manual procedure for setting the idle (jumper the diagnostic box to put it into the set mode). That sets a fixed idle speed solenoid duty while you adjust the air screw.
05-16-20, 09:20 PM
