Here is the run down. I have a 1992 2.2 placed in a 72 Squareback. I am using a "Enginewiring.com" VSS simulator. On initial start ups and subsequent trials at idle there did not appear to be any issues. The only odd thing to note was the fan would kick on and off with the key on at the same point the fuel pump kicks on. At trail start ups, it would idle up appropriate to the temp indicated, and slowly idle down as it warmed up. The fan would kick on at 200 and off at 190. This is without any exhaust or an O2 sensor and only idling in the driveway.

Then the first drive. Let the car warm up to operating temp. Everything was normal. Drove one block. Didn't see or hear anything out of the ordinary.

The next morning, weirdness starts. The first thing noted was that the fan kicked on and the idle jumped up really high very early during initial warm up. This only last a minute or so, before the fan turned off and the idle dropped back down. I let the car continue to run and was paying close attention because this was so odd and different. When the temp reach about 160 the idle jumped way up but the fan didn't kick on this time. After a minute the idle dropped down again. Now I was really wondering what the heel was up. Sat there watching the temp and waiting. Temp gauge finally hit 190, no fan but idle jumps way up again and stays running high at approx. 900 - 1000 RPM. Temp gauge gets to 200 where the fan normally kicks in, but no fan, still idling really high. I wait 205, no fan, fast idle. 210 no fan, so I shut it down. That's not it, now it wont start. WTF!!!!!! Just in case you were wondering, this all occurred at a start up and idle in the driveway without driving. It only was around the block that one time. Push it into the garage and wait for tomorrow to see what happens next.

Next day. Starts after a big hiccup. Start up repeats the above. Hits a fast idle with the fan kicking in very early. Idles down once operating temp reached. Idles up once well after warm up, no fan. Reaches 190, no fan, idle jumps up and climbs to over 205 without the fan kicking on. Note I can get the fan to cycle on and off before starting the car with the key in the on position, same point where the fuel pump kicks on and primes.

Reset. Unhook the battery and unplug the computer. Wait a few days. Repeat. Car doesn't start after being shut down during high idle. WTF!!!!!! When it does start, gives a big hiccup almost a backfire. I can smell gas when trying to start during this time.

New tactic, reset the computer. Test different ground wires. Note a wire that I labeled ground for AT transmission codes. Unusual things that occur with this ground are; during normal idle causes car to idle very low, approx 400 RPM. During high idle causes car to idle down to almost a normal idle, but can tell it is a touch high. Try the same with wire labeled ground for neutral switch codes. Note the car this came out of was a manual. Needless to say, no of the trails above solve the issue, it still idles fast when temp reaches 190+ and the fan doesn't kick in??????? Wont start if shut down during the fast idle, and smells of gas.

So I play with the grounds and turn off the car before it hits the high idle points. I let the fan cycle before start up and start the car at a point where the temp gauge is at 190 and I get the fan to cycle on and off as it should when and where it should. WOW, what a pain in the ass. Let the car idle and run. Fan continues to perform as expected. On at 200 and back off once temp drops to 190. Idles smooth as butter. No jumps in idle, and fan cycles as normal. OK we are back to normal.

Next mistake. Take the car for a short run up the block. Notice temp gauge creeping above 205. Turn and scat home, coast down the hill into the driveway, WTF!!! high idle and fan not kicking on. Temp at 205+. Shut it down. Wont start again.

I think it is a VSS issue and not a ground. I was able to get it out of this high idle and fan not working cycle until I took it on a second drive. This appears to be the cause of this weird idle and fan not kicking on when temp reached 200 F.

Any thoughts after reading this. I tried to give all the info to help. The wire harness was done by myself. Stock computer. Reversed intake manifold. Heater bypass loop in place. Before the first drive I thought that I had completed a conversion without a single problem related to idle, fans, cooling and anything electrical.

Do you have you CEL connected, are there any code flashes? Can you extract the codes from the ECU? otherwise you are just shooting in the dark.

I do have a CEL but it has never flashed any codes that I am aware of. Thought I had it connected correctly? Can I check for codes off of the ECM any other way?