doctorj77

So I picked up a 95 GTS last month with only 56k on it. Car has been very well taken care of, not a ounce of rust anywhere which in MI is hard to do. Car runs great. Has Edelbrock Performer Intake [Upper/Lower] & Performer .190 Heads. BBK 65mm TB, Ford Motorsport stainless shorties and a E303 cam. Car runs good, makes good power, but I did notice two things

1. To get going in 1st gear you really had to get the rpms up to take off. Having cammed cars in the past, I figured that was characteristic of the setup.
2. Gas mileage was rotten. I'm getting 9-10mpg. That just didn't seem right. Yeah the gears were upgraded to a 3:27 but that's not that aggressive
3. Kept hearing a mystery noise, not ticking or grinding, but more like a grinding. But definitely wasn't from the engine.

As I got more familiar with this car, I have discovered the following

3. The Air diverter and Air bypass solenoids coming off the smog pump were not connected to anything
4. As I went to install a CAI, I found a vacuum harness (Red / Green / Grey / Tan) coming out of the fender well, not connected to anything and not capped
5. Identified the EGR was incorrectly hooked up. It was directly connected to the intake with a random piece of black vac line. As I read into this, that told me the the EGR was wide open at idle - WOT

Corrective actions taken

6. Figured that the EGR was dirty from the way it was hooked up, I removed it. I hooked it up to a vac pump, it held just fine. I then moved onto cleaning it up really good. Reinstalled with a new gasket.
7. After some online research, I connected the Red line to the EGR solenoid, Green line to the Intake, Grey to the Air Diverter valve, and Tan to the Air bypass valve
8. Drivability improved significantly. Taking off in 1st gear was no longer labor intensive, however I could still hear that mystery noise mentioned earlier
9. Diagnosed the grinding noise was the smog pump. Since I just installed a O/R H pipe, I figured I no longer need this. Bought the delete kit and removed the pump. Capping off Grey/Tan vac lines from the harness & line running to back of the passenger side head.

Results

10. As mentioned before, drivability was very improved. But since I fixed the EGR, i noticed that my base idle was a little too high, like 1200-1300. As I drove the car, coming to a stop I noticed the rpms come down rather slowly, and sometimes surge up to 1500-1800 before coming back down, verrrrrrrry slowly.
11. In addition I now periodically get a noise in the dash, Almost sounds like a blend door having trouble actuating. I tested the HVAC, from Max AC - Defrost, everything works just fine. I can switch hot/clod with no issues.

Starting to chase down the idle surging issues and have led to the following

12. Removed the IAC and tested it. Verified it works by hooking it up to a pwr source. Seemed to work, but was very dirty. Cleaned it up using carb cleaner and reinstalled.
13. Checked my TPS and verified am receiving .98v at idle. I have not tested this under load yet.

After cleaning up the IAC nothing really changed. Idle still hangs

14. For S&G I decided to replace the IAC. Comparing the two parts side-by-side, using a volt meter I tested for resistance. The old one read 12ohms. The new one read 10ohms. Suggets the coil on the old is weeker than the new one. Put the new IAC on but left it disconnected.
15. Followed procedure for setting baseline idle. Disconnected battery for 30min and reconnected. Started vehicle and adjusted the idle stop screw on the TB to 1000rpms. Followed by adjusting the idle air bleed valve, ensuring it was less than 2 turns to close while maintaining the desired idle speed. Reconnected the IAC, and no change (as expected) in the idle, hovering right at 1000rpm. Turned on the AC, it dipped maybe like 50rpms and recovered quickly. The IAC was doing its job.

Proceeded to drive the car and noticed the following

16. Still periodically getting that weird noise in the dash. Seems to only last for 3-5sec each time.
17. After the car warms up and is driven, notice the RPMs still seem to hang around 1200-1300 for a little bit before dropping down to 1000.

Aside from that, the car runs and drives fine. Eliminating the common EGR, IAC and TPS related symptoms, leads me to believe its vacuum related now. I'm going to put a gauge on it this weekend to test, but before I do, can anyone suggest what vacuum dependent items are inside the dash that might be causing the noise? Initially I was thinking a vacuum canister or the EGR vacuum solenoid might be the culprit, but those are in the passenger fender well. There might be a leak in a vac line for sure, but the line itself wouldn't make this noise, its a component that's doing it. This noise is almost directly centered, like its directly behind the radio, or at the back of the engine. I'll try to upload a video of it this weekend. But curious if anyone else has experienced a similar symptom.

wbrockstar

Look at the vacuum tree on the driver fender apron and you'll see a black, 1/4" vacuum hose with a rubber boot on it.This hose runs from the vacuum tree to the area behind the upper intake where it connects (via a plastic vacuum splice) to another vacuum hose thats coming out of the firewall,beside the ac evap core tubes.The hose section that disappears into the firewall runs to a port on the back of the heat/ac control panel.This feeds vacuum to the control panel & the panel has numerous other ports on it that distribute vacuum to several components behind the dash.A
vaccum operated actuator opens and closes a door that directs airflow out of the vents,floor or defrost vents.The actuator is most likely what you're hearing move along with the hissing of a vacuum hose?? The pictures below show which vacuum hose Im referring to on the vacuum tree port.If you wanna check to see if a vacuum hose is causing the noise,remove the hose at the vacuum tree or disconnect it at the plastic vacuum splice,plug the hose or the vacuum tree port (depending on where you disconnect the hose) then start the car & let it idle or drive it to see if the noise has disappeared.If it does disappear,that verifies a hose is leaking or possibly disconnected,since
the noise stopped once you removed/ plugged the hose.The heat/ac will usually come out of the defrost vents only,if this hose has either issue above. If this hose is ok,one of the other hoses may be leaking between the control panel and an actuator, which sounds more likely since the noise is coming from behind the radio.A vacuum motor may be present too?? It might be behind the glovebox?? An actuator should be present towards the left side of the hvac housing??

The pictures & diagram shown below may help.The black vacuum hose thats part of the vacuum hose assembly, shown in the last picture below,is the hose that you can see coming out of the firewall.The other hoses connect to actuators or vacuum motors behind the dash.

doctorj77

Awesome info WBROCKSTAR........ Thank you for sharing that. I did step through a few a couple other things over the weekend, temporarily deleted the EGR system. Did some testing and concluded the EGR Vacuum Solenoid was faulty. Before I dropped $35-45 on a new one, decided why not try deleting the EGR system. Car actually seems to be running better without it ironically. But that mystery noise was still present so I'll follow your info and try to track it down this week.

Thank you again

wbrockstar

Are you sure its running better without the egr valve or is it possible the egr valve was opening at the wrong time and disconnecting it seemed like it made the car run better?? Its only supposed to open during cruise mode,so if it was opening during idle,acceleration or wot,temporarily deleting it would have made it run better.Excessive carbon buildup,a leak in the diaphragm,reversed vacuum hoses at the evr solenoid or a defective evr solenoid are things that would cause the egr valve to stay open continuously.When its open the exhaust gases lower combustion chamber temps & the ecm leans the fuel mixture and adds timing advance,which causes reduced emissions,less chance of pinging & a possible small increase in fuel mileage.

doctorj77

Well didn't find the leak yet. BUT I did confirm that the red line does a Y-pslit in the wheel well. One end goes to my EVR, and the other goes into the firewall. So I could only imagine it was for the heater. As it turned out, I had my EGR vacuum lines reversed. The red line was hooked up to the EGR and the green to the intake.

I did a basic vacuum test and that's when I discovered I wasn't getting any vacuum through the EVR solenoid. Once I figured out the lines need to be swapped, no more random noise under the dash

dawson1112

You mention that you have rev it up high in first gear to take off, I wonder if it has an aluminum flywheel in it. Because they are lighter than the steel ones they don't carry as much momentum. The steel ones have alot of momentum behind them to help get the car moving with less rpms.