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Ok I got lazy and now I think it bit me in the rear end.
Ok to make a long story short I recently replaced my tired twins with stage 3 bnr’s. I bought a a gasket kit that included the lower intake gasket. So while the turbos were out I removed the upper intake and unbolted the lower intake manifold and noticed to much crap was still attached so not wanting to remove all the fuel and some vacuum lines I pried the lim just enough to remove the old lim gasket and installed a fresh new metal factory gasket in place. Torqued everything back up including the twins and now I have a high idle. I tested with a homemade smoke machine and can’t find the fking vacuum leak anywhere. What do you guys think went wrong? Could it be my lazy butt not removing the lower intake manifold all the way and doing the lim gasket the right way? I just don’t know we’re to look. I checked just about every vacuum line with no luck plus the smoke machine test. I did find some cuplers were leaking on the smic and also a leak on the throttle body. The leak on the throttle body is coming right we’re the tps bolts up. I know vacuum leak occur right after the throttle body so all the leaks I found should not give me a high idle. Let me know what you all think. Thanks in advance guys |
Interested in this because I just did the exact same thing
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Did you have a metal or paper LIM gasket before this process?
I've experimented with smoke machines but I've always had better luck with a can of starting fluid. Spray it where you think the link is, if the engine revs up, that's the spot. Did you have to remove either of the fuel rails in the process? The grommets at the base of the fuel injectors like to go missing really easily. If you had a paper gasket, it's possible there's still a piece of it and it's keeping the LIM from sitting flat. As I think you've figured out, a vacuum leak can only be between the throttle body plates and the engine. It doesn't take much to increase the idle. I would probably pull the upper intake manifold and give everything a thorough going over before going medieval and pulling the lower. Could be something dumb like the ground wire that goes around the rear stud where the UIM meets the LIM is between the two manifolds instead of on top. Dale |
Years ago, I purchased an FD. A dealership told the owner he needed new turbos because they were glowing due to a high idle. I had difficulty determining what the problem was. I suspected a vacuum leak but could not find it, even though I sprayed carb cleaner all over the place. Later when I placed a cd jewel case over the end of the black intake tube and the engine continued to run, I was convinced it was a leak. I was able to locate the leak with carb cleaner. If I remember correctly with the jewel case was still on. In this case the lim gasket was missing pieces. |
I just removed and reinstalled the LIM and UIM with new ones. One thing that could cause a vacuum leak on the LIM is mixing up the bolts. The lower two are 25mm but the upper three are different, two are 55mm and one is 45mm. The 45mm won't typically be long enough to bite in the 55mm spot, but if you tighten the other two first you can get a few turns of the 45mm to bite in the 55mm hole, which could easily loosen later. Also, remember there are two vacuum hoses on the side near the block, one that goes to the lower Y-pipe connection, which cannot be dislodged easily since it is clamped down, but can crack easily if brittle, and the other smaller hose going to the fuel regulator, which is easy to pull off the LIM.
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Also, I forgot to mention that my 45mm bolt was actually 50mm long, likely was replaced with a non-stock slightly longer bolt.
Mike |
Originally Posted by DaleClark
(Post 12276711)
Did you have a metal or paper LIM gasket before this process?
I've experimented with smoke machines but I've always had better luck with a can of starting fluid. Spray it where you think the link is, if the engine revs up, that's the spot. Did you have to remove either of the fuel rails in the process? The grommets at the base of the fuel injectors like to go missing really easily. If you had a paper gasket, it's possible there's still a piece of it and it's keeping the LIM from sitting flat. As I think you've figured out, a vacuum leak can only be between the throttle body plates and the engine. It doesn't take much to increase the idle. I would probably pull the upper intake manifold and give everything a thorough going over before going medieval and pulling the lower. Could be something dumb like the ground wire that goes around the rear stud where the UIM meets the LIM is between the two manifolds instead of on top. Dale |
Originally Posted by mikejokich
(Post 12276870)
I just removed and reinstalled the LIM and UIM with new ones. One thing that could cause a vacuum leak on the LIM is mixing up the bolts. The lower two are 25mm but the upper three are different, two are 55mm and one is 45mm. The 45mm won't typically be long enough to bite in the 55mm spot, but if you tighten the other two first you can get a few turns of the 45mm to bite in the 55mm hole, which could easily loosen later. Also, remember there are two vacuum hoses on the side near the block, one that goes to the lower Y-pipe connection, which cannot be dislodged easily since it is clamped down, but can crack easily if brittle, and the other smaller hose going to the fuel regulator, which is easy to pull off the LIM.
not OP but related question, after I put everything back together and drove around, I have this tapping sound coming from somewhere in the engine bay. I also was lazy and did not entirely remove my UIM, just pulled it up to access the intake air temp sensor. could I have dislodged anything that makes a rhythmic tapping sound? It almost sounds like a tapping valvetrain on a piston engine. I also did not replace my metal UIM gasket, as it seemed to be in fine shape. don't know if it's related, but I also changed spark plugs and moved spark plug wires around at the same time. car seems to run strong and normal though. |
mkiv98, the tapping could be a plug wire that's not on good and it's arcing to ground. Should be easy to see.
FYI the metal lower intake manifold gaskets pretty much never fail. It's worth changing if you're rebuilding the engine and it has crazy miles on it, but otherwise not worth doing. As evidenced here :). The different length *bolts* are for the lower intake manifold to engine, not the UIM to LIM. I would pull the UIM and do a thorough look around. If you did anything with the air control valve that's an easy way to make a vacuum leak. Try the starting fluid test as well. Dale |
Originally Posted by DaleClark
(Post 12276950)
mkiv98, the tapping could be a plug wire that's not on good and it's arcing to ground. Should be easy to see.
FYI the metal lower intake manifold gaskets pretty much never fail. It's worth changing if you're rebuilding the engine and it has crazy miles on it, but otherwise not worth doing. As evidenced here :). The different length *bolts* are for the lower intake manifold to engine, not the UIM to LIM. I would pull the UIM and do a thorough look around. If you did anything with the air control valve that's an easy way to make a vacuum leak. Try the starting fluid test as well. Dale |
We are getting this thread off-track, may want to work on it a bit and then post up a new thread.
Dale |
Originally Posted by DaleClark
(Post 12276950)
mkiv98, FYI the metal lower intake manifold gaskets pretty much never fail. It's worth changing if you're rebuilding the engine and it has crazy miles on it, but otherwise not worth doing. As evidenced here :).
Dale Hey Dale the reason I went ahead and replaced the the lim gasket because of the unknown mileage of engine. I had the fking thieves at Aspec (when they were still in business) replace my engine with a suppose Mazda reman engine. I payed them a lot of money for a simple reman engine and they gave me my car back with a used engine that they probably removed from a customers car that probably upgraded their engine. When I got my car back I was missing a lot of parts of my car, oil pan has a big dent and was leaking oil, the sensor on the oil pan is broken not plugged in, twins had exhaust leak and so as the down pipe. So to get to the point, I know that they did not replace a single gasket with my $7,000. That’s why I went and replace just about every gasket I get the chance to replace when doing work on the Fd. I will do the carb spray method this weekend and will report back. Thanks Dale |
I had a similar issue when I went with a single turbo. I took off the LIM just enough to get the old gasket off and put the new one on. The old one was a paper gasket and a piece ripped off when I took it off. I didn’t notice and put it all back together and had a high idle. I ended up finding it by blocking off the down pipe and making an adapter that went over the turbo to pressurize the system. Sprayed soapy water everywhere and ended up finding it on the LIM to block gasket. |
All of the throttle bodies on these things leak around the throttle shaft when you smoke test, so there's no problem there.
Wouldn't say the metal LIM gaskets never fail either, ended up with intake vacuum leak, high idle and fuel down the block on one a few years back, shouldn't be an issue with a new one though if installed correctly. Problem comes reusing them a couple of times - now resorting to using goop even when they're new, to be doubly sure. I might try plugging the tailpipe and putting the smoke up the exhaust instead of the intake side, otherwise I expect you're up for removing the turbos and LIM if you can't see anything obvious up top, there's 5 bolts and 2 nuts from memory on that manifold too. |
Ok wasted a whole can of flammable brake clean and could not find a single vacuum leak. I did not get a noticeable idle change. What else would cause a high idle? I am lost here, I sprayed in between the twins and lim and under the uim with no noticeable change in idle. The engine is currently idling at 2k so not sure if it’s a small vacuum leak that is not causing a big change in rpm when spraying the brake clean. Used brake clean because it’s flammable and had it on hand by the way. |
I had a thought, which is probably a long shot, but did you in some way change your throttle cable length either by shifting the location of the cable, crimping the cable or something else. Take off your throttle cable end at the throttle body and make sure your dashpot is not stopping your throttle return and start the car. Just a long shot possibility.
Mike |
A high idle can ONLY be caused by air getting in. You have to find where the air is getting in at.
- Throttle body not fully closed, either from a misadjusted cable, fast idle cam not doing what it should be doing, or someone messed with the throttle body stop. - ISC stuck open - it bypasses air around the throttle body. If it's jammed open or something that will cause a problem. - Vacuum leak as stated. It is somewhere between the throttle body and the engine. Check gaskets, block off plates, the hose to the vacuum booster, etc. Also I do prefer starting fluid to brake clean. It evaporates way faster, burns better, and comes out in a nicer mist. Dale |
Originally Posted by mikejokich
(Post 12280334)
I had a thought, which is probably a long shot, but did you in some way change your throttle cable length either by shifting the location of the cable, crimping the cable or something else. Take off your throttle cable end at the throttle body and make sure your dashpot is not stopping your throttle return and start the car. Just a long shot possibility.
Mike |
Originally Posted by DaleClark
(Post 12280387)
A high idle can ONLY be caused by air getting in. You have to find where the air is getting in at.
- Throttle body not fully closed, either from a misadjusted cable, fast idle cam not doing what it should be doing, or someone messed with the throttle body stop. - ISC stuck open - it bypasses air around the throttle body. If it's jammed open or something that will cause a problem. - Vacuum leak as stated. It is somewhere between the throttle body and the engine. Check gaskets, block off plates, the hose to the vacuum booster, etc. Also I do prefer starting fluid to brake clean. It evaporates way faster, burns better, and comes out in a nicer mist. Dale |
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