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View Full Version : unplugged IAC and car does nothing



ghostryder
06-18-2014, 05:34 PM
car is idling very low in reverse and drive went to adjust idle according to prior post. so I unplugged the IAC and nothing idle didn't change high or low or shut off. do I need a new IAC or TPS?

also how do you adjust the throttle stop screw?

anyone with any suggestions on either problem ?

thanks

KMT
06-18-2014, 05:43 PM
What year is your SC?

My '90 has a throttle plate stop screw but not an adjustable air bleed screw.

S_Mazza
06-18-2014, 08:41 PM
I doubt that the TPS, IAC, or throttle stop is your problem.

How low is low, anyway? What RPM?

Did it just start suddenly? Did the car sit for a while? Was other work done?

Can you check the fuel pressure?

Can you check the timing with a light?

XR7 Dave
06-18-2014, 09:12 PM
Way too much not enough information to help. A little background to the problem would go a long ways.

ghostryder
06-18-2014, 10:26 PM
I doubt that the TPS, IAC, or throttle stop is your problem.

How low is low, anyway? What RPM?

Did it just start suddenly? Did the car sit for a while? Was other work done?

Can you check the fuel pressure?

Can you check the timing with a light? when I drive it idles at 1k rpm when put in drive it drops to just below 500 and surges to around 700 same when put in reverse. fuel pressure gage says 36lbs. other work done is replaced engine and tranny mounts, fuel injectors pcv valve and replaced all the vacuum hoses. I checked them all for leaks and none also checked the ic tubes and no air leaks. has brand new battery and starter. car sat for the winter months. haven't checked the timing

XR7 Dave
06-19-2014, 08:58 AM
Since you have not said otherwise, I'll assume the engine is completely stock and that it ran fine before you took it all apart and changed a bunch of parts. Or did it? It's not normal to change injectors, so I guess the first question is why you did that, and did you change injector size? Second question is, how did you determine that there are no leaks? Did you perform a smoke test? If not then there are no assurances that a leak is not present.

Generally speaking plugging/unplugging the IAC will result in a change in idle but if you have other issues it can mask the true culprit. It's pretty easy to swap an IAC and you probably have one laying around so I would have probably done that first. Otherwise another way to see if the EEC has learned bad data is to disconnect the battery and then see if it acts differently when you start it back up.

ghostryder
06-19-2014, 02:58 PM
Since you have not said otherwise, I'll assume the engine is completely stock and that it ran fine before you took it all apart and changed a bunch of parts. Or did it? It's not normal to change injectors, so I guess the first question is why you did that, and did you change injector size? Second question is, how did you determine that there are no leaks? Did you perform a smoke test? If not then there are no assurances that a leak is not present.

Generally speaking plugging/unplugging the IAC will result in a change in idle but if you have other issues it can mask the true culprit. It's pretty easy to swap an IAC and you probably have one laying around so I would have probably done that first. Otherwise another way to see if the EEC has learned bad data is to disconnect the battery and then see if it acts differently when you start it back up. engine is completely stock. when I bought it wasn't running the owner before me said the injectors were bad so I replaced them all to be on the safe side. replaced them with stock injectors. some of the vacuum hoses were cracked and brittle so I replaced them all and zipped tied them to their connection points. had engine pressure tested and it was in great shape. supercharger tubes have new Teflon gaskets. I have a brand new battery I disconnected it and let it sit for a day. hooked it back up this morning started it up and it does the same thing. I ordered a new tps and iac waiting for those to come. Could the EEC-IV be the problem I read a few post and some mentioned that it controls the idle?

thanks for being patient

XR7 Dave
06-19-2014, 04:08 PM
Doubt it has anything to do with the TPS, but you can easily check that with a volt meter. The signal wire should rest at about .9v and rise to about 4.75v when you open the throttle, key on, engine off.

The IAC could be stuck closed which would be consistent with a previously non-running engine. This would explain the high idle in park and low idle in drive/rev.

If the IAC isn't the problem then it goes back to vacuum leaks. Teflon gaskets do not ensure a leak free seal, in fact they can be the cause of leaks. If the IAC doesn't fix the issue then a smoke test is next.

ghostryder
06-19-2014, 04:31 PM
thanks. iac and tps will come tomorrow hopefully that fixes it.

ghostryder
06-20-2014, 08:09 PM
Doubt it has anything to do with the TPS, but you can easily check that with a volt meter. The signal wire should rest at about .9v and rise to about 4.75v when you open the throttle, key on, engine off.

The IAC could be stuck closed which would be consistent with a previously non-running engine. This would explain the high idle in park and low idle in drive/rev.

If the IAC isn't the problem then it goes back to vacuum leaks. Teflon gaskets do not ensure a leak free seal, in fact they can be the cause of leaks. If the IAC doesn't fix the issue then a smoke test is next. replaced the IAC today the idle dropped. In park its stays between 500 and 1k mark. took the Teflon gaskets off and put rubber o rings on IC tubes. now the problem is when in drive or reverse and I step on the brake the idle drops below 500 and the car shakes excessively how can I fix that problem? also I have a brand new battery and my battery light is on constantly do I have another issue?

XR7 Dave
06-20-2014, 08:47 PM
A lot of people on here use the teflon gaskets and most have good success. However, I know from past experience that this is not always the case which is why I mentioned that they can cause issues. I did not go into detail on any recommended solution, but the rubber 0-rings is not the right solution. I did recommend a smoke test to see if and where you might have leaks. There are many places that an SC intake system can leak, in fact they are too numerous to list. I recommend you put the teflon gaskets back in and then have it smoke tested. This will definitively locate any possible leaks.

I still don't know what year your car is or if it has EGR, but a sticking EGR valve can definitely cause idle issues too, so don't overlook that.

Stock idle speed is 550rpm in drive and 700rpm in neutral and our tach's are notoriously inaccurate, but in any case it should not be shaking so it seems clear that something is not quite right.

ghostryder
06-20-2014, 09:14 PM
A lot of people on here use the teflon gaskets and most have good success. However, I know from past experience that this is not always the case which is why I mentioned that they can cause issues. I did not go into detail on any recommended solution, but the rubber 0-rings is not the right solution. I did recommend a smoke test to see if and where you might have leaks. There are many places that an SC intake system can leak, in fact they are too numerous to list. I recommend you put the teflon gaskets back in and then have it smoke tested. This will definitively locate any possible leaks.

I still don't know what year your car is or if it has EGR, but a sticking EGR valve can definitely cause idle issues too, so don't overlook that.

Stock idle speed is 550rpm in drive and 700rpm in neutral and our tach's are notoriously inaccurate, but in any case it should not be shaking so it seems clear that something is not quite right. its a 1990 automatic and no EGR. I will put the Teflon ones back on. I will do the smoke test this weekend.


any recommendations on why the battery light is still on after I start the car.

XR7 Dave
06-21-2014, 09:48 AM
Unless you have a wiring issue, typically that means the alternator voltage is less than battery voltage. I've had some alternators that won't start to charge until you rev the motor up a bit - like 2500rpm or so. If this is the case then you know it's not a wiring issue and just a funky alternator. Otherwise if you have a voltmeter you can check output right at the alternator. Sometimes the fusible link can get blown at the solenoid, which is why I never assume that the alternator is bad when the light is on, although the light being on does usually indicate a bad alternator.

figulaz
06-21-2014, 12:23 PM
Does your car have a brake booster? I see where part of the problem shows up is upon braking. I did a conventional conversion on my auto and had a used booster with serious vacuum leak hiss. I swapped in a new one from rockauto and it was great for a week and then developed some hiss (but thats another thread). Try listening for booster hiss if you hear it try plugging the vacuum line to the booster to see if it helps idle ...of course dont drive it. Good luck. Let us know the results of the smoke test too.

ghostryder
06-21-2014, 08:53 PM
Unless you have a wiring issue, typically that means the alternator voltage is less than battery voltage. I've had some alternators that won't start to charge until you rev the motor up a bit - like 2500rpm or so. If this is the case then you know it's not a wiring issue and just a funky alternator. Otherwise if you have a voltmeter you can check output right at the alternator. Sometimes the fusible link can get blown at the solenoid, which is why I never assume that the alternator is bad when the light is on, although the light being on does usually indicate a bad alternator. it was the alternators and I replaced it now light is out. thanks

ghostryder
06-21-2014, 08:54 PM
Does your car have a brake booster? I see where part of the problem shows up is upon braking. I did a conventional conversion on my auto and had a used booster with serious vacuum leak hiss. I swapped in a new one from rockauto and it was great for a week and then developed some hiss (but thats another thread). Try listening for booster hiss if you hear it try plugging the vacuum line to the booster to see if it helps idle ...of course dont drive it. Good luck. Let us know the results of the smoke test too. no booster still has abs going to convert it this week to conventional