boostin13b

I'm pulling my hair out and going crazy over this problem. I just dropped in a known good engine that I purchased from another board member. I dropped it in my car, 99% bone stock. Stock twins, stock intercooler, stock everything pretty much. Only things not stock on the setup are a downpipe, k&N filters, and a SSQ BOV. Everything else is stock.

Problem.....I start the car cold.....starts right up, fast Idle like it should, I drop it down manually, or let it finish, same result either way. Idle drops to 1500 when up to temp or dropped manually. The second I put the car in gear, idle falls to around 800 (Where it should be) has a huge miss it feels like and dies. It doesn't drop when I push in the clutch like it's the clutch switch dropping the idle, only when I put it in any gear. So my Idle is messed up pretty bad I know. Vacume is around 14 inches when Idling at 1500 and droppes to 8 inches or so when idling at 800. Almost like huge vacume leak opens up when I put it in gear. It always seems like it has a miss slightly when idling. The engine will almost pulsate, but not so much that it shows on the tach.

Now when it's hot, it will not start, almost like it is flooded, but the plugs are not wet or fouled. Giving it gas does not change a thing. Fuel pressure is holding, injectors are not leaking down. FP Solenoid is working correctly. The car will start once it cools for a few minutes, but will run really bad and idle horrible, I have to keep it running for a little bit until it will idle back to 1500 on it's own.

I have replaced the coils, no change. I'm getting good spark to every plug. Compression test is fine. 8's across the board. Engine has about 20K I was told. Plugs are new. I've pulled the manifold off a couple of times and all vacumes are new and attached. So the car is acting like it has a vacume leak somewhere because of the 14 inches of vacume. I know it should be around 18 or so.

I can't find any intake manifold gasket leaks with carb cleaner. I'm wondering if there is a solenoid sticking open causing a leak, but even if there was I shouldn't have these large of problems, it should still start half way decent when hot and idle better.

The TPS voltages are good, and there are no codes stored. I've tested pretty much everything I can think of at the moment. I'm just wondering if anyone else has had this type of problem. The only other thing I can think of right now is maybe the ignitor is not working properly. But I'm getting good spark. I might try to swap it out with another local FD to see if that changes anything. I'm just at a loss right now and need to pass emissions to get my plates, I just got a ticket for expired tags this morning.

Any help would be great.

boostin13b

Oh yeah. Car boosts fine and runs great besides what I described above. I'm getting perfect 10-8-10 boost pattern, no smoke or hesitations. Very strong and runs like a champ otherwise.

dubulup

thats sounds like a pretty weak motor

boostin13b

That's what it seems like, but the compresion is great. It's not eating coolent, I've pressure tested the cooling system. It's not eating too much oil.

dubulup

a vacuum leak after the TB will increase rpm, increasing vacuum. 8in-hg is pretty low.

a vacuum leak before the TB won't affect idle.

DaveW

You've diagnosed it correctly - you have a relatively LARGE vacuum leak. The hot-start problem is probably also due to the leak, since less fuel is normally required for hot start, and this mixture is diluted too much to ignite by your vacuum leak.

You may just have to start looking at all the joints and hoses that relate to the manifold. There may be something that you can't get carb-cleaner spray to reach. Also, if the PCV valve sticks open, it will cause a large leak.

boostin13b

I'll have to take a look at the PCV today, I've been so stressed about this I didn't even think about that. Thanks, I'll let you know what I find. As for a leak somewhere else, I'm pretty sure I covered about everything around the manifold.

BlueTII

You need to pull the engine codes, if you do not know how here is a link to a "how to " on our website. http://www.banzairacing.net/FD&S5_error_codes.htm
What you are describing sounds like a bad water thermosensor

ptrhahn

iTrader: (9)

I would replace the 02 sensor, or turn the 02 feedback off (PFC), and check/replace both the ISC and the wires to it.

I had some similar problems, and first it was a loose wire to the ISC... that fixed some of it (high, or erratically uncontrollable idle), but it still ran rough, low vac, etc.... turned the 02 feedback off in the PFC, and it INSTANTLY gained 2" of vaccum, smoothed out, settled down, etc.

boostin13b

There are no codes. I've tried pulling them. And just to make sure Everything is working, I've pulled off sensors to set a code and it will set a code. So I know there are no codes stored. I've also hooked it up to my snap on scanner and still nothing.

As for the water thermosensor, it doesn't seem to be the issue. I'm getting a right reading from it.

I do not have a PFC so I have no way of turning the 02 feedback off. Sensor seems to be reading correctly as well. Not sticking or slow in anyway. I'm getting the same signal to the ECU as well, so I know there isn't any break in the wiring somewhere.

boostin13b

Update......

Looks like I may have some bad but confusing news. After going over everything multiple times, and checking the PCV and everything else. I pulled the valve out of my manual compression tester and threw it in. Looks to me like the rear Rotor is no good. I got 35-40 psi pulses. But they are dead even. Then on the front rotor, I got 60 psi pulses all even. So i've pretty much come to the conclusion that I have a bad engine.

I'm going to try another real compression tester to see forsure, because I'm guessing the one I borrowed from my buddy at Mazda seems to have a problem with it since it gave me all good readings.

I'm kind of confused as to why I'm getting even pulses out of the rear rotor though. I would expect to have 2 dead spots and one at least a little higher. I'm trying to figure out why all 3 faces would have the exact same low compression number. If it threw a seal and took out all 3 faces, it wouldn't have that good of compression and wouldn't run as well as it does under boost. I also tried the ATF trick and same results.

Now I'm wondering if I talk to the guy I got the engine from and try to get my money back or if I just sell the whole car. I don't have much time to work on it because I'm always working on everyone elses cars everyday. I have a spare builder engine that I pulled out of it that I'm thinking about building, but I just don't have the time, and don't want to spend the money to have someone build it when I could do it myself just fine.

DaveW

Scored housing? That would give similar low results on all 3 rotor faces.

boostin13b

I was thinking about that. Or even if it was not assembled right to begin with. Wrong tolerances. I was told it only has around 20K on it, and the block looks fairly clean so I don't doubt it. Maybe if the side housings or one was out of tolerance, or a corner seal took out the corners? I just don't know what to do at this point.

boostin13b

Something strange happening today. I seem to be building more vacume in different areas. A little more at idle, and it's pulling more on decel. I'm wondering if I have a couple stuck Seals. I did add ATF to the low compression rotor, I wonder if it's freeing something up. It also seems to have more vacume when the air pump is engaging or disengaging, I can hear it click, then I see the vacume build, then click again, and vacume drops. I wonder if the BAC is sticking as well?

wstrohm

Stick a light under the front of the UIM and see if the ACV vacuum control hose is pinched by that low spot under the UIM. That was the one thing I did wrong when reassembling after a vacuum hose job, and it caused (sort of) similar symptoms to yours. Once I rerouted that hose, everything ran (and runs) very smoothly. No clue regarding the low compression on your rear rotor, though.

boostin13b

I'll have to check that out as well, I'm sure I double checked all that stuff like 10 times, but who knows. I'm trying to get a hold of a good compression Tester to get the final verdict of the rear rotor, and I will go from there.