Hello Everyone,
Like so many other users on this post, I wanted to say thanks to everyone for their input. I normally don’t sign up for different forums, but I found this so helpful I needed to say thank you as well as add what I learned from my experience of doing the infamous GM Lower Intake Manifold gasket (IMG) repair.
All the advice I found on hear was right on and very helpfully in getting prepared for the long task in front of me.
In short the two things I learned in addition to the advice given here is, triple check which gaskets are for your specific application, since most of the gasket kits include multiple gaskets for different GM engines. Make sure you old one’s line up exactly with your new one, I did not do that and ended up with a vacuum leak. Also, like everyone else stated, make really detailed notes on where your wires go, and I recommend taking the time to paint a couple of your items.
Here’s the long story. In addition to everyone’s recommendations I also replaced all my water/heater hoses, the overflow tank ($23 rockauto.com) my radiator ($83 delivered from radiatorbarn.com), the belt tensioner pulley and idler pulley also got replaced. Also because you are tearing down so far and are taking the time to clean everything and remove all the carbon deposits from your lower and upper intakes, I also picked up a can of Chevy Orange engine paint ($6). I sprayed the valve covers and the upper intake, it’s not a 350, but it sure looks cool. When I was at the parts store getting more coolant to top off after the job was complete it made everyone do a double take at my little family car.
In addition to thanking everyone for posting their knowledge, I wanted to add a couple things I learned from the project as well as maybe help those three other people I saw on this thread looking for help with a vacuum leak after replacing their IMG gasket. After completing all that work, cleaning the compartment real nice and painting the upper engine she started up great, but would not idle. My first thought was the lower gasket did not seat correctly and I had a vacuum leak, but I also thought it was possible I damaged a sensor or broke a hose and or wire. First I tested the throttle position sensor (TPS) and got a resistance of 1.9ohm at 20 OHM setting. I replaced the Idle Air Control (IAC) valve because it was loaded up with carbon deposit. I knew the throttle body was cleaned very thoroughly but none of these things solved by idle problem. To make things more difficult I had no OBDII codes thrown, which felt kind of good, but at the same time gave me no leads. I had replaced the PVC, the hoses to and from the PVC (including the u shaped one on the EVAP purge valve) I also replaced the PVC 90 degree elbow with a spark plug boot due to the old one crumbling in my hand. I put all the old part back on (duck taped the broken ones) and the vacuum leak continued. Next I unplugged the EGR and the car idled, it idled rough, but she ran. I was certain it was the EGR, I could only find articles on how to test is with a hand vacuum pump, but not with a multi-meter. I replaced it anyways, and my problem remained. Finally I tested EVAP purge valve (connects to EGR and PVC hose), I got a resistance of 0.3 ohm at 2k OHM setting, I knew that was good. My fear was I had to tear down again.
I knew for sure I had a vacuum leak, I just couldn’t find it. I decided to start the re-tear down, at least to the top intake manifold. First I sprayed starter fluid around all the lower and upper intake gaskets, if the engine revved up I would know where my problem was, nothing. I was kind of glad, but also more confused.
Then started the tear down. I Started removing the throttle body, air box, coil packs, etc. I asked my friend who was a huge help if he saw how the throttle body intake gasket looked, his response was “what gasket?” We found the gasket still attached to the throttle body (TB), it was hanging cock-eyed on one bolt still after removing it, but my friend noticed that the gasket partially covered up a nook on upper part of the throttle body. How he saw that I don’t know but we looked at all the gaskets that came in the kit, and two of them were identical except for one gasket had a slight cutout for that notch on the throttle body. The mistake I made was I placed the “new” throttle body gasket over the old one and said yup the holes line up, the outside looks the same, and the hole in the middle is the same. What I couldn’t see was I was also covering up a small notch in the old gasket that allowed air to get to the EVAP purge system, hence we were choking the vacuum and the car would not idle. We replaced the TB gasket, bolted everything backup and she purred like they day she rolled off the GM lot.
Another mistake we made was, we did not realize the male connector on the end of the fuel injector harness needs to come back out under the upper intake on the passenger side. It naturally wanted to lay and come out on the driver side. Instead of tearing down the upper intake, we cut the connector off, spliced in some wires to the length we needed. Taped the whole thing up, then got some wire loom to protect it, taped up the wire loom, then zip tied it along the metal coolant line back over to the passenger side of the motor to reconnect it.
In the end everyone comments on here allowed us to do a phenomenal job, other than out two mistakes it was a huge success, and I must admit that Chevy orange paint job on the valve covers and upper intake looks awesome against the black wire looms, black hoses, and the black oil cap.
In addition to what other have taught me about doing the IMG gasket, I hope others learn that they need to triple check which gaskets in their kit goes to their car. I believe my kit included gaskets for the 3.1, 3.4, and maybe the 3.8 used in several front wheel drive Chevy’s, Olds, Buicks, and Pontiacs. Even though I thought I paid attention to people notes about marking everything, clearly I should have put more labels with meaningful notes on where the wires should go.