Removed and Reinstalled UIM, now hard to start/idle.
 

Two nights ago I removed my UIM to replace the Throttlebody Coolant Hose that goes from the Rear Iron to the Throttlebody as well as the coolant hose underneath the throttlebody.

After a relatively easy swap, I checked to make sure everything was secure and proceeded to reinstall the UIM. After I thought I was finished, I started the car and it ran like ass. The idle was unstable, showed low vacuum, and didn't rev properly. Assuming I messed up somewhere, I removed the UIM a second time to check for Vacuum leaks and what not.

After replacing a few questionable hoses, I reinstalled the manifold again and started the car. Again it was hard to start, idled even worse, and pulled the same amount of vacuum (25mmHg according to PFC) The throttle needs to be depressed for the car to come on, it will sometimes idle by itself, but not for long. I put my hand infront of the TB elbow (intercooler not connected) and it does pull vacuum but it just doesn't sound good. Motor shakes and vibrates when you rev it.

I have spent two days troubleshooting and searching the forums for keywords such as vacuum leak, leaks, vacuum, idle, starting, UIM, throttlebody and I am still stumped.

I have checked every vacuum hose in plain sight (yes the MAP hose is connected). All bad or even marginally questionable hoses have been replaced with Baker Precision Silicone hose.

The car ran flawlessly before I took the UIM off, I just wanted to replace the throttlebody coolant line because it looked sketchy and I figured it would be a safe thing to do... =/

Mods (though I dont think it should matter):

1993 FD3S Base

APEXi PFC
BNR Stage 3 Twin Turbo - Sequential
GReddy Profec Type S
M2 Med Intercooler
GReddy Throttlebody Elbow
RB Catback


I usually don't resort to starting my own thread, but I am stumped. Can someone help me out? Possible connectors I forgot to hook up, sensors to test, hoses I forgot to connect?

btw, all sensors check out properly on the PFC commander, nothing is out of spec. Spark plugs shouldn't be fouled, they were replaced about 500 miles ago. Fuel Filter replaced 300 miles ago.

My references for this whole project:

http://www.rx7.org/Robinette/manifold.htm

http://www.rx7.org/Robinette/hoses.htm

map sensor hose not connected?

This is my guess.

^sorry guys

I didnt see anything about the gasket between LIM and UIM if its a paper one it could have torn without you noticing.

It is possible that you knocked the tps out of adjustment. I would test/adjust it and see what happens.

UIM/LIM Gasket is metal and in good condition.

Yes, MAP hose is connected.

Thanks but still need help. =/

Recheck your work. Re-do all the steps you did and inspect. Most likely, if you remove the UIM and re-install it; whatever you missed last time you'll connect up the second time. We can't tell you what you missed or messed up since we don't know exactly what you did. If it worked before, then it's something you did so retrace your work.

Make sure ISC is connected, I forgot that once and it idled rough.

I have the manifold apart right now, and this would be the fourth time its all apart. Whatever it is that I changed the first time, was changed unintentionally, as in I accidentally messed with it while taking off the manifold the first time. That's why I'm wondering if there's anything that I could have messed up without knowing while taking off the manifold.

Yeah it was connected all three times.

I'm going to try testing the TPS according to the FSM.

You replaced the coolant line to the rear iron? Did you check to see if you knocked off anything for the fuel pressure regulator? You just really need to start shining lights in there and making sure everything that should be connected, is...

25? you sure it's not at least 250?

Yes coolant line from TB to Rear iron. I did disconnect one of the fuel lines back there to gain access to it but it was one of the first things I reconnected during the initial re-assembly. I didn't think it would be a fuel problem because the car seemed to be getting fuel, but I will check all the fuel lines back there just to make sure.

22~25 mmHg is what the PFC says. The Autometer SportComp Boost gauge varies from 2~10 inHg. Both PFC and gauge were working accurately before, with readings of ~410mmHg / ~16inHg at idle.

Keep in mind the car does not idle stable, it surges randomly and the vacuum readings on the autometer gauge surge with it. The PFC vacuum/boost readings however stay at a constant 20 - 30 mmHg, with or without throttle.

I've been staring at this mofo for a couple of hours and I can't find anything wrong with the UIM/TB/ or rats nest. everything looks solid. Could a hairline crack in one of the rats nest vacuum hoses even cause this much disturbance in the idle? I feel like I need to have a massive vacuum leak for the car to idle this bad.

stumped....:scratch:

rig up a pressure tester with PVC and a pneumatic fitting. Fighter's garage used to sell one. basically you plug one turbo inlet and then pressurize the other. Look at the example here for a 300zx Twin Turbo: www.boostpro.net/prodtester.html

Sounds like a vacuum leak.

If you reverse the gasket between the TB and UIM you will have a vacuum leak! the notch on top of the gasket must be on the firewall side. Good luck

I just tried rigging something like that up today with a PVC cap attached to the TB Elbow and hand pump but I couldn't get the system to hold pressure, like at all. It wouldn't build even half a PSI. I don't think my pump moves enough air to pressure the whole intake manifold + motor before it all leaks out.

Do the rotor chambers even hold pressure with motor not in use? And what kind of pump should I be using to pressurize the chamber? I am currently using a standard hand pump connected by silicone.

Weird thing is, I never removed the TB from the UIM, I just took off the whole thing as one piece. The notch WAS AWAY from the firewall. I just checked, removed, and replaced it with the notch the other way today. However the car ran well before, pulling great vacuum with the notch the other way, and I can't really see how that notch plays a part in sealing the TB to the UIM. So I'm not sure that's going to solve the situation, but I tried it anyway.

---

I replaced 1 more vacuum hose since my last post, its not that it needed replacing, its just because I could pull it off, so I figure might as well switch it to vacuum. I'm going to reattach everything and try it again. I feel like the problem is electrical but all the PFC sensors read within range and I just tested the ISC according to the FSM and it is in spec.

Also I forgot to mention that while doing the coolant hose, I decided it would be a good time to replace the FD Fan thermoswitch with the FC one, however I still doing think that should make a difference since the thermoswitch should only affect when the fans come on and not what the ECU sees to adjust AFRs.

Well I got a little bit of progress today. The idle can now support itself as long as I don't rev the motor, and I am pulling 250~290 mmHg. I'm not sure what it was because I took lots of things apart and put it back together. However it still runs like crap, backfires at the throttle let off, and if I let off the throttle too aggressively, the engine will kill itself.

Here is a video of the idle and what not -

http://www.youtube.com/watch?v=s6g2A3Gb4XQ

Idle - 620 RPM
Vacuum - ~280mmHg on PFC/ 9inHg on Boost Gauge
Inj Duty Cycle @ idle - 5.7% (2% higher than normal)
AFR - ~16.7 (innovate WB, as engine rpm increases to 3000, AFRs go up to 19, I am running Stock Air Pump and Cat)

I have the Idle Air Screw at half turn from all the way in, while the car was running I did try to adjust it but it looks as if it made no difference in the way the car ran at all.

I'm gonna have the manifold off one more time and take a real good look at everything, but I seriously can't figure out what it is.

Have you made sure the check valve that goes to the MAP sensor is installed correctly?

IT'S NOT A CHECK VALVE, it's a filter. People keep thinking it's a check valve.

Dale

Air goes through both ways, so yeah its not a check valve. I have ran the car with the filter arrow pointing both towards the MAP and away from the MAP and it made no difference when running the car. The vacuum hose diagram does have the arrow pointing away from the MAP so that's how I have it now.

Thanks for everyone's input, but keep them coming. Car is still broke :(

Just to explain... difficult to see but the gasket is embossed on one side only
http://i39.photobucket.com/albums/e1...3A1-13-655.jpg
http://i39.photobucket.com/albums/e1..._1916661_n.jpg

Good luck!

Thanks for sharing, I had never noticed this before. I suppose there is a 50/50 chance I reinstalled this correctly the last time it was removed from the car.

Don't feel bad. Taking my UIM off before I've broken the tb to elbow oring, had check valves disintigrate in my hands, broken solenoid nipples, etc etc. It's always an adventure. Removing the UIM the last time led to a complete vac hose replacement, but it was time for that anyway. Shortly after that it cold start munched an apex seal leading to engine replacement. On the plus side it led me down the "replace all the old crap" path and now it's running great *knock on a pile of wood*

Did you check your harness for any plugs that might have backed out of the connectors, I've had that happen too.

You didnt install this incorrectly. The distance from the bolts from left to right are different from the top 2 and the bottom 2. The gasket wouldnt even go on the 4 bolts if you had put the gasket upside down.

I had a somewhat similar issue the last time I removed the UIM. My idle was hunting all the way to about 3k rpms and would not hold steady. Adjusting the idle screw changed nothing. I had ended up changing the pre tension on the throttle cable when I removed it. So I ended up tweaking the tension on the throttle cable to get it almost perfect and using the idle screw to fine tune it.