So today I fired her up to go to work and had a strange issue. I could hear a hissing noise and my rpms sat firmly at 1000, and on top of that.. my speedometer didnt work. The car drove fine but the SES light was pegged on. So I drove to work, at idle 1000 rpms on the dot. When I pulled into the parking lot at work and put it into Park, the rpms surged up to 2000 for a moment.. and after 10 seconds sitting there, I shut the car off. I figured, vacuum leak for the hissing so I looked at all the vacuum hoses and nothing seemed abnormal.

I check the codes, and nothing! I fired it up and it was gone. A few hours later I got a moment and went outside and fired it up, again no issue.. I had the hood popped and I wiggled the wiring on the IAC and TPS and it came back. I think this happened to be coincidence as you will find out further down. Also this time, there was no hiss.. just the high rpm and bad speedo. I turned it off and tried to pull the codes but the darn thing would NOT go into diagnostic mode. The SES light was on, the fans came on like it was in field service mode.. but the SES light didnt flash whatsoever. So I had to get back inside and a little while later I came outside.. and it went into field service mode.. AGAIN no codes.. and AGAIN, it fired up and didnt do it. I wiggled those same wires and it did nothing this time. Im all sorts of confused.

Maybe I should mention that recently I changed the pigtail on the IAC as it was broken around the plastic pieces going around the metal connectors. Ever since I changed that pigtail, the car would idle a little funny.. like the RPMs would surge between 500-700 at idle in Drive, but NOT in park. Also the voltage on the in dash gage would surge in sync with the rpm surge. Weird? I also noticed a ticking noise(above the normal tick) that seemed random and I have not yet been able to track down the source of this tick.

I have swapped the optispark in the last few thousand miles, changed the intake gasket due to the oil leak in the back, the ignition coil, the ICM, and done the spark plug wires twice within a few thousand miles. I had rerouted them the proper way when I did the distributor as I had never noticed the brackets that ran behind the power steering pulley when I originally did them.. but they popped out of those brackets(the wires were 8mm and not 7mm so they did not fit properly) and got cut partially through by the serpentine belt causing a poor idle. When I changed them, the issue was gone.. then a few days later I did the IAC pigtail and have been having the surging issue ever since.

Any suggestions :P

EDIT: Oh the two wires to make the OBD1 to USB came in and I got that all connected/soldered up.. and yesterday, I plugged the car up to Scan9495 and ran the car. All the values seemed to be normal. I pulled up a list of "normal tech-1 idle values" for the 93 and it seemed like all voltages and sensor ranges were within the acceptable ranges. I did notice that sometimes the knock count and knock retard would flash up a random number but it would usually go away and Im getting no other indication that its actually having a knock. The unusual tick I mention there didnt seem to coincide with any of the scan values on the program. The only code I get consistently is 32-EGR. I also noticed while running the car on the DTC section sometimes random codes would flash up for a brief instant then go away.. nothing staying there with any consistency beside 32. I havent had a chance to hook it up with the most recently speedometer/idle issue yet but I will in the morning when I get off work. I saved the data from the brief bit of recording I did with the program the other day. I will upload it and if anyone is familiar with that program, could you take a look at the file and see if you can see anything abnormal?

Edit 2: Ok on the drive home, a couple symptoms that are evident.

1 - I tried to hook up my laptop and run Scan9495 for the ride home but the diagnostic port is not functioning with whatever issue this is despite the SES being on from key on. With key on engine off, the fans engage. I have a manual fan switch and I verified a number of times that it was in fact off.

2 - In park, car idles roughly 1800-2000 on the dot. In reverse, overdrive, drive, and 2.. it idles at 1000 rpms. I unplugged the vacuum hose to the EVAP from the EGR and that had no effect. Also unplugged the vacuum hose from the throttle body to the evap, no effect.

3 - While driving, I gunned it for the hell of it and when the engine reaches 3000 rpms.. the car sputters a bit. It doesnt necessarily bog down, you can hear it cutting power and regaining power very quickly/rapidly.. like 5 times per second the power cuts out and kicks back in and it makes a very interesting/unique sound.

Im going to putz around with it some more today and we'll see if I cant figure this out. I have a spare used TPS, MAP, and IAC I think Im going to try.

 

Here is the file if anyone familiar with the program has a few free minutes. During this recording, the idle in drive surge from 500-700 rpms was present but not the speedometer/rpm issue. Thanks again guys

 

Nevermind guys. It was the vacuum lines going to the EVAP being old and crummy. Im an idiot. Have a nice day guys

 

lmao,,, self service works on this site. good to hear you got it figured out.

 

Well, apparently I dont have it figured out. When I thought it was one of the EVAP lines earlier today, it just so happen that one of them popped out really easily. One other thing that I did do was turn off the heat and restart the car. Then a few hours later I went for a spin and turned the heat back on.. When I got back I restarted the car to move it and it came back. This time I had a suspicion that it might have something to do with it so.. again I turned the heat off and it started back up normally. Apparently the heat is causing this issue and Ive only recently replaced the heater core so Ive never run into this problem. Any ideas why the heat might be causing this interference?

I can RUN the heat, but I just have to make sure its set OFF before I run the car again. Weird :P

 

there is a vacuum line to the heat control. the vacuum line is on the passenger side of the engine and comes out of a wire harness. you might try unhooking it and plugging the line on the engine side.

 

http://shbox.com/1/hvac_vacuum.jpg
my 93 does not have the check valve, at least i dont recall ever seeing it.
http://shbox.com/1/vac_check_valve.jpg

 

could also be the tps is failing, iac motor/valve may also be sticking or in need of cleaning.

 

Back to report, AGAIN, heat being on/off was just coincidence. The issue is still occurring intermittently. Because of the intermittent nature of things, Im having a hard time tracking down the source. It seems to occur only at times when I cant actually take a look ie- firing it up to go to work or getting off work at 6am and it being dark as hell and 45 minutes from a decent jack and jack stands to get under it if need be.

I will say this though, I have removed the TPS and cleaned it up twice now in the past week. When I did the intake gasket, I did the entire TB gasket set including the IAC housing and that top cover and all the surfaces were cleaned until they were literally spotless. I spent like 3-4 hours JUST cleaning the TB, IAC housing, and that top plate. I did not remove the IAC valve itself though I think Ill do that today if I can. This issue only began to occur after I replaced that IAC pigtail and perhaps the force from pushing the pigtail in and out started this. Also did the TB bypass cause I figured thats one less potential spot for coolant to leak and destroy my opti.. so the coolant ports on the IAC housing are plugged with vacuum caps.

My only question then, if it does indeed turn out to be TPS, IAC, or something of that ilk.. is.. Why would that effect the diagnostic port and the speedometer?

 

has the computer been tuned? take the ecm out and see if it has a chip added. brb