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In preparation to tune-up my 1987 C4 Convertible 5.7L engine, I decided to clean the throttle body myself. I have worked on engines before and the Army made certain that I would never forget the benefit of doing the work myself. After reviewing the steps and making certain I was familiar with everything, I had an easy start but a few surprises along the way.

In the first picture, you'll see my engine compartment. From right to left, Air intake duct (front), MAF, Air intake duct (rear) Throttle Body and TPS.

After inspecting everything, I disconnected the Air Intake duct (rear) from the Throttle body, using a flat head screwdriver to loosen the clamp. The duct had apparently never been taken off before and was tough getting loose but I worked it back and forth until it was loose. After getting the rear duct loose from the Throttle body, I found the MAF sensor connector and removed it and unclipped the MAF from the front duct. By removing the MAF as well as the rear duct, I ensured I had clearance/access to the coolant hoses.

With the air intake duct removed, I had better access to the TPS and IACV sensors. When I removed the TPS sensor connector, I discovered that the TPS sensor was cracked (bad news) and needed to be replaced. It was much tougher to get my fingers under the TPS and coolant hose to gain access to the IACV sensor underneath the Throttle body. At first attempt, I removed the clip holding the sensor wires to the connector. I reconnected this and with a little more effort, worked the IACV sensor connector loose.

The TPS sensor connector is the 3 port plug and the IACV sensor connector is the 4 port plug in the center of the picture.

I moved to the driver's side of the engine and located the throttle connections. I had been warned of the 'Jesus clips' (so named because they have a habit of getting lost during removal). So, I placed a white shop towel below the throttle connections before working on these. The outside throttle connection was pretty easy but the inside throttle connection was a bit tough as it was below the throttle body and behind the Throttle body coolant hose. You can see the 'Jesus clips' on the top of the engine block and the throttle lines in the middle of the picture.

With the sensor connectors removed and the throttle cables removed, it was time to remove the coolant hoses. These proved to be quite challenging as the throttle body coolant hose was in a tough spot. I ultimately had to remove the coolant circulation hose from the radiator as well as the EGR sensor connector to gain better access to the connections on the Throttle body. I like that the connections were tight and the hoses were in good shape but I had to be cautious not to get over excited here. I worked the hoses back and forth until they finally came loose and radiator fluid began to drip from the throttle body. With this step complete, I was ready to unbolt the Throttle body from the engine.

With everything I could access removed or disconnected, I loosened the throttle body bolts. There is one bolt per corner. I loosened the top left bolt first, then the bottom right, then top right and finally the bottom left (left being passenger side). I don't think it really matters on sequence but I didn't want to find myself with the bottom bolts pinched by the weight if I removed the top bolts first. As I pulled up the Throttle body, I found the small vacuum tube on the bottom and disconnected it. The effort took me a little over 15 minutes to complete.

With the Throttle body removed, I took it to a bench and examined it for damage, rust, cracks, etc. The only damage was the cracked TPS, which I removed and set aside. Because I wanted a clean TB and IACV, I decided to remove the IACV coolant cover from the bottom of the Throttle body.

Upon inspection, I noticed that the 6 hex head screws/bolts were rusted as well as the entire underside of the coolant cover. I applied some 'break free' hoping that this would resolve the problem. Unfortunately, it didn't. Of the 6 hex screws, 4 heads snapped off and the other screws came out with little effort. Fortunately, because the screws snapped off at the head, once I removed the coolant cover loose from the Throttle body, I was able to use a vice grip and additional break free to remove the remaining 4 screws.

I sat down with an old toothbrush and some Throttle body cleaner and began to clean the throttle body venturas, the exterior to the throttle body and the throttle spring. Once the throttle body was clean, I cleaned out the IACV coolant cover being careful not to get any of the cleaner in the IACV. I used the toothbrush to clean the area around the IACV but spent most of my time on the rust and coolant sludge in the coolant cover. I took a little time to clean off the coolant scale from the hose connections and did a final inspection before taking a break to find a new TPS and some hex screws. Total time to complete the cleaning was about an hour. Cost, including the new TPS, gaskets and a couple of new hose clamps was less than $100. I was able to find a TPS at Autozone but I've delayed looking for the replacement hex screws until I do some research. Although I could probably find something at Ace hardware, I'm hesitant to pick any screw for fear of stripping the threads on the Throttle body. Plus, it gives me more time to check the cooling lines and connectors before reinstalling everything and setting finishing the tune-up.

I'm including a copy of the throttle body parts from the manual for everyone's reference. Good luck.

I reviewed the following notes to prepare for my DIY adventure. Although it said nothing about the risk of rusty hex head screws/bolts or cracked TPS, it provided enough detail to warn me of the pitfalls of the 'Jesus clips, the underside vacuum hose and being careful with the IACV.

Here is what the final product looks like. It went from dark sooty crud inside the venturas as well as yellow slime in the IACV coolant cover to a shiny silver for the Throttle body and rusty (but clean) IACV coolant cover.
 

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Iron Fist in a Velvet Glove
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Good job!

Steven
 

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Discussion Starter #3
Coolant cover torque screws

Just an update. After some review, I found that M4 bolts from Ace worked fine as a replacement for the broken IACV Coolant Cover bolts. Because the area has a habit of rusting, I stringly recommend using a washer on each bolt. This also helps if the bolts are a bit longer than the original. An added plus is that the bolts were anodized steel, which should reduce corrosion.

Off to inspect hose connections while the Throttle body is still off. Once that is complete, time to re-install Throttle body, adjusting TPS and completing the tune-up.
 
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