Cak119 Posted August 20, 2016 Report Share Posted August 20, 2016 I have a 98 deville with 197k miles on her. For starters the plugs and wires have been changed, new fuel filter, changed iac valve and throttle positing sensor. Usually it takes 2 to 3 turns of the key to start her. Once started she is usually idling at 1000 rpm or higher. If I drive off like that she just keeps increasing in speed. So if she is that high I shut her off and turn back on. Usually idle is at 2000rpm so I shUT down again and turn back on, usually 3rd try or longer she is finally idling around 600 to 675 rpm. When driving she is usually good but every so often all of a sudden rpms increase and she starts gain speed without giving gas. Sometimes hitting the pedal a few times will work and she will go back to where she should be other times I have to pull over shut her down and restart until the rpms are correct. Since the iac valve and the position sensor have been replaced, what could be causing all these issues? Thanks! Chris Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 20, 2016 Report Share Posted August 20, 2016 The very first thing to do is to check for trouble codes that have been set by the on board diagnostic system. Go to the bottom of my post here and read how to check codes. Write down codes and post them here. Restart the system over as much as you need to write down the codes. Be sure to write down whether the codes are History or Current. Then and only then will we be able to help you because we will have guidance. Otherwise we would be guessing. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
rockfangd Posted August 20, 2016 Report Share Posted August 20, 2016 Welcome to Caddyinfo. You should have a code present and even a light. Sounds like it needs a idle relearn after the IAC has been replaced. What was the reason for the replacement of the IAC? GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
Cak119 Posted August 20, 2016 Author Report Share Posted August 20, 2016 Rockfan the iac was changed because that is what the guy at autozone said was probably causing the issue. Bobby, I can't find where it says how to check the codes at the bottom of your post Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 20, 2016 Report Share Posted August 20, 2016 Cak119 you must be using a smart phone, its not on mine either, it shows on the laptop. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 20, 2016 Report Share Posted August 20, 2016 Cak119 you must be using a smart phone, its not on mine either, it shows on the laptop. This should help. You have an on board diagnostic system that saves codes for the powertrain, body, chassis, abs, tcs, suspension, ipc, and ac, and others. You do not need autozone anymore retrieve the codes and post them here and we will help. Use your smartphone to video tape them and play it back later to write them down. Here is how to retrieve them and if you go to the OBD2 link you can see what they mean. I gave you a cadillac history link also 1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
rockfangd Posted August 21, 2016 Report Share Posted August 21, 2016 So you had the same problem before the IAC was changed? I wonder if your throttle body gasket is bad and leaking between the spacer and the throttle body. Was anything done with the throttle body or intake lately? I ask this because it is possible to put the TB gasket on backward and that will cause problems like what you describe GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 21, 2016 Report Share Posted August 21, 2016 It is probably a vacuum leak, the question is whether its a one or two bank leak. (P0171 and or P0174) It could be a dirty throttle body plate and or throat holding the plate open. That probably wouldnt set code other than P1525 Throttle Body Service Required, which I got on my 96 when it was dirty. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Cak119 Posted August 21, 2016 Author Report Share Posted August 21, 2016 I just pulled the codes. It won't let me upload the video so I will go write them down and post. Yeah it was doing it before we changes iac and it didn't help. Throttle body has not been taken off lately or intake. Thanks wI'll post codes shortly Link to comment Share on other sites More sharing options...
Cak119 Posted August 21, 2016 Author Report Share Posted August 21, 2016 P0102 history P0103 history P0440 current P0603 history P1602 current P1644 history B1552 history U1255 current B2120 history B1656 history U1300 history B2148 history Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 22, 2016 Report Share Posted August 22, 2016 DTC P0440 Evaporative Emission (EVAP) System DTC P1602 Knock Sensor (KS) Module Performance Those are current codes, no lean codes thats good. These codes should not cause the high idle. We can worry about them later. The U network code might be related to the knock sensor. I would remove the snorkle and clean the throttle body really good, the throat and the plate including the back and edges of it. Hold it open, by holding the lever near the accelerator cable. Use a lint free rag and GM upper engine cleaner. Dont pour or spray anything into the throttle body. This job can take 20 minutes to do a good job. Wear rubber gloves, start there. When you are done disconnect the negative battery cable for a couple of minutes ro "reboot" the system and reconnect. See if that helps Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Cak119 Posted August 22, 2016 Author Report Share Posted August 22, 2016 Okie dokie, thanks. Do I need to replace the knock sensor? Also my traction control light is on and my antilock brake light is on. Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 22, 2016 Report Share Posted August 22, 2016 Reread my post i edited it a bunch of times. I dont think its the sensor itself. Has the starter been replaced? Are those all the codes? I am not seeing any suspension or abs codes... Maybe the current network code is related to the suspension. I am in the car, I cant look at the manual Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Cak119 Posted August 22, 2016 Author Report Share Posted August 22, 2016 Those are all the codes that came up. I have never replaced the starter, idk if the previous owner did or not. Link to comment Share on other sites More sharing options...
rockfangd Posted August 22, 2016 Report Share Posted August 22, 2016 You may have a issue with the harness atop the engine. Do a visual check at the wiring that runs on the passenger side by the intake, follow the battery cable under the intake. Then look at the harness to the throttle body area. Also to my knowledge IAC failure is not not very common but rather mistakenly replaced and causes more problems. A new IAC needs to learn the proper idle positions, whether cold start, warm start, ac on or off, rear defroster on or off. All of these things control the idle via the IAC valve. If the position is not learned it will randomly idle higher and higher, until the key is recycled a number of times. I call it self driving. It starts to rev up a little and just goes up from there. normal warmed up idle with ac off is around 600-650 rpm no ac. 650-700 rpm with ac on GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 22, 2016 Report Share Posted August 22, 2016 Thanks Rock, that is what I was trying to do, by having him disconnect the battery, thx Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Cak119 Posted August 22, 2016 Author Report Share Posted August 22, 2016 I saved the old iac. I can put it back on if you think I need to. Link to comment Share on other sites More sharing options...
OldCadTech Posted August 22, 2016 Report Share Posted August 22, 2016 I think we're mixing diagnostics here. 98 Deville, IF IRC is an Idle Speed Control motor it physically pushes on the throttle linkage. - IAC is an Idle Air Control... it opens or closes an air passage to allow or restrict air past the throttle plate Two different systems. Are we mixing nomenclature? I think the ISC can be reset in overrides, if I'm not mixing my models but I think 98 Deville had overrides THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!! Link to comment Share on other sites More sharing options...
rockfangd Posted August 22, 2016 Report Share Posted August 22, 2016 All of mine have IAC. Right near the TPS. There is a port for it. Not related to the throttle cable. Unless I am missing something. Can be seen in this picture above the TPS. GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
Logan Posted August 22, 2016 Report Share Posted August 22, 2016 That is a IAC valve set up. The ISC system should have gone away with OBDII. Other GM vehicles have been using the IAC style for over 10 years before Cadillac switched over. Logan Diagnostic LLC www.airbagcrash.com www.logandieselusa.com www.ledfix.com www.ledfix.com/yukontaillightrepair.html www.ledfix.com/ledreplacements.html www.ledfix.com/j42385toolrental.html Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 22, 2016 Report Share Posted August 22, 2016 Currently I am working on a 95 with an ISC and a 98 with an IAC. My 96 had an IAC. As Logan notes, the ISC ended with OBD1 Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
OldCadTech Posted August 22, 2016 Report Share Posted August 22, 2016 Sounds like 95 was the magic year and I had em reversed. I'm headed for the woodshed, for my beating.... THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!! Link to comment Share on other sites More sharing options...
Cak119 Posted August 25, 2016 Author Report Share Posted August 25, 2016 Took the throttle off took some pictures of the inside but the pictures are to big to load. There is some fluid pooling right in the opening of the engine. Throttle was very dirty. Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 25, 2016 Report Share Posted August 25, 2016 31 minutes ago, Cak119 said: Took the throttle off took some pictures of the inside but the pictures are to big to load. There is some fluid pooling right in the opening of the engine. Throttle was very dirty. If you see black gunk inside the intake its ok, as the guru used to say, oil vapors from the egr system condense and accumulate there. Glad to hear that the throttle body was very dirty my guess is that was your problem. Be sure you clean the IAC port and seat. If you want to post photos use photobucket, dl the app. Upload the photos there and link them as an image here. Easy Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Cak119 Posted August 27, 2016 Author Report Share Posted August 27, 2016 Cleaned it all up also put old iac on. So far she idles perfect at start. Driving great only tried speeding up once I hit the gas and she came right back down. Next issue lol when starting for the 1st time of the day or if sitting for over an hour she take 2 sometimes 3 times to start, also a little rough sometimes at starting then smooths out. Mpg has been around 10 Mpg. The gage that says what I've used is always different from the actual fuel gage. Always says I've used less than what actually has been used. Link to comment Share on other sites More sharing options...
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