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Username Post: 86 Caprice high idle problems        (Topic#89019)
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
01-27-05 05:08 AM - Post#611004    

Hey all. First time poster here. I'm hoping you all can help me out. I have an 86 Caprice Classic, 305, and I'm having problems with incredibly high idle on my car. The car starts without issue, but once the thermostat kicks in, the idle speed on the engine cranks up quite a bit.

I've replaced the PCV Valve, O2 sensor, fuel filter, coolant temp. sensor, thermostat and water pump recently. The problem's getting progressively worse. I have to stop the car when in drive to avoid unstoppable dieseling. However, if re-starting the car after turning it off, the idle sometimes returns to normal. Additionally, the check engine light comes on SOMETIMES when sitting at a light or bumper-to-bumper traffic during the work week commutes.

I've considered the Idle Air Control, but I can't seem to locate it on the throttle body. Is this something that can easily be pulled off, sprayed with some carb cleaner and replaced with little incident? Or do you all suspect something else? I'm open to any and all suggestions, as my avg. gas mileage went from 15 - 17 MPG to 10 - 11 MPG.

Thanks in advance!

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 




good.wrench 
Chevytalk Staff
Posts: 20079
good.wrench
Loc: new york,usa
Reg: 03-30-01
Re: 86 Caprice high idle problems
01-27-05 08:11 AM - Post#611005    
    In response to Ronnie Bass

ronnie the culprit is the IAC VALVE,it's located on the passenger side of the throttle body and slightly toward the back,it has a huge nut fitting on it,the connector that fits it is a 4 wire square type connector,unscrew it from the throttle body and replace it,i further recommend you locate the aldl test port just under the dash,jump togther terminals "A & B" turn on the key,it will flash the check engine light 1 flash then pause then flash twice then pause,that is the ready to test signal,after that it will flash all the codes in memory then when that is done it will again flash code 12 signifying the completeion of self test,look up the codes to see what they are and replace whatever is bad. incidentally,the "NEW IAC" will learn the saettings from the computer,do not try to adjust it,it has a gasket too so don't lose it.

good.wrench
c/t staff

84 S-1O 4x4 if your poor your crazy,if your rich your eccentric!


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
01-27-05 09:19 AM - Post#611006    
    In response to good.wrench

Thanks for the quick response! I'll make it a to-do this weekend, for sure. My old man is an old-school mechanic and said that I could clean the thing, but I'm a purist in the sense that I like to have as little doubt as possible when it comes to problem correction. I'll give your suggestion a try and let you all know the results.

I looked up the price of ALDL gauges online and found they were in upwards of $300. You think most auto parts places would have one to fire up in the parking lot, or is it even worth buying it?

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
good.wrench 
Chevytalk Staff
Posts: 20079
good.wrench
Loc: new york,usa
Reg: 03-30-01
Re: 86 Caprice high idle problems
01-27-05 10:23 AM - Post#611007    
    In response to Ronnie Bass

you don't need any test equiptment,your car is equipped with the obd1 computer system,that means it has a built in self test and diagnostic system,it shows you by way of flashing the yellow check engine light,it flashes for example code 22 which means 2 quick flashes then a pause followed by 2 more quick flashes which means code 22 which just happens to mean the throttle position sensor but this is just an example,go to this site,it shows you what the test port looks like and which terminals to jump to flash the check engine light.as for the IAC valve that is a motorized valve,when they quit working they are usually burned out,replace it but before you do clean the inside of the tbi housing it goes into,they get sooty and gummy in there.

obd1 testing

good.wrench
c/t staff

84 S-1O 4x4 if your poor your crazy,if your rich your eccentric!


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
01-28-05 06:25 AM - Post#611008    
    In response to good.wrench

Getting frustrated with part searching on this thing. I spoke with the local Chevy parts dealership and they said they only see a secondary air control unit. In describing it to me, it's definitely not the part I need. Most other local auto parts chains say they see it but it has to be ordered from the dealer. And one parts store even said that 86 Caprice's didn't have IAC valves on them.

Could someone straighten out this mess for me? From the thread, it's better to replace than clean, but I'm finding it hard to find a replacement. Is this unusual for this particular part? Let me know.

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
good.wrench 
Chevytalk Staff
Posts: 20079
good.wrench
Loc: new york,usa
Reg: 03-30-01
Re: 86 Caprice high idle problems
01-28-05 07:41 AM - Post#611009    
    In response to Ronnie Bass

go to this picture,does this look like what you have? or do you have a carburetor? which?

tbi unit picture


this is what the IDLE AIR CONTROL VALVE LOOKS LIKE

IAC VALVE

good.wrench
c/t staff

84 S-1O 4x4 if your poor your crazy,if your rich your eccentric!


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
01-28-05 01:24 PM - Post#611010    
    In response to good.wrench

That first picture looks nothing like anything on my car. My car is carbuerated. From the reading I've done, IAC valves are only found on TBI models. If that's the case, what kind of model am I on, and what else could be the problem with my high idle?

Thanks for the pics, BTW.

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
good.wrench 
Chevytalk Staff
Posts: 20079
good.wrench
Loc: new york,usa
Reg: 03-30-01
Re: 86 Caprice high idle problems
01-28-05 03:05 PM - Post#611011    
    In response to Ronnie Bass

ok,now we know that you have a carburetor,there are three things that will cause a very high idle
1. choke not fully opening,bad choke thermostat or out of adjustment

2. main idle stop adjustment set too high
3. secondary barrel throttle plate not closed all the way resulting in air flowing through the secondary causing a very fast high idle

look in the top of the secondary barrel,if the throttle plate isn't closed you will see it,that normally only opens above 55mph but they have been known to pop open if you goose the pedal too hard,they get dry from lack of lubrication,lubricate all moving carb linkage parts

check the main idle stop set screw adjustment,if it's improperly set the idle cannot drop back to normal idle,some carbs have a solenoid that steps up the idle when cold or when defrost or a/c is on,they get out of adjustment,you need a manual to adjust that.

the choke thermostat opens the choke fully vertical when the engine is fully hot,if it isn't then it's either out of adjustment or the heating element is weak or bad

sometimes a vacuum leak can cause it to rev fas as well,you need to check,lubbricate and adjust any of the things i've told you,let me know how it comes out,go and buy a manual for that year car so you can see in fuel/carb system how to adjust and know what is what.i cannot show you myself,it would require too many pics and a lot of written instruction,the manual gives you everything.

good.wrench
c/t staff

84 S-1O 4x4 if your poor your crazy,if your rich your eccentric!


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
01-29-05 08:00 AM - Post#611012    
    In response to good.wrench

I've got a manual for my year car already (which is why I suspected the IAC), and I'll make it a point to go through the fuel delivery system to learn it and try to make sense of it. Thanks for the info, and I'll be sure to post after I take a look.

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
good.wrench 
Chevytalk Staff
Posts: 20079
good.wrench
Loc: new york,usa
Reg: 03-30-01
Re: 86 Caprice high idle problems
01-29-05 09:16 AM - Post#611013    
    In response to Ronnie Bass

ok ron,i posted the tbi pictures and the iac picture so that you would know if they are what is on your engine,if not you might have a quadrajet or dualjet carburetor on there.

good.wrench
c/t staff

84 S-1O 4x4 if your poor your crazy,if your rich your eccentric!


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
01-31-05 05:35 AM - Post#611014    
    In response to good.wrench

The top plate of my carb looks similar to this picture:

http://alanhorvath.com/54chevy/chevypics/rochester.jpg

The surrounding mechanisms aren't identical, but the top plate is exactly like mine. SO much stuff to fiddle with on it, I'd be scared to pull it. I've got a carb cleaning bin in my garage at home, but I wonder how much trouble it is to pull the carb, clean it and replace it. Can it be done in a weekend? Maybe she just needs a running over?

As far as the parts listed in the previous posts, can any of those be replaced or overhauled? Is there anything that I can do to ensure a better running engine? There are a few things that appear to stick or just not cooperate in general when I checked out the carb this weekend. Any ideas? How about the choke thermostat? Is that something that can be replaced or overhauled? Maybe I should just buy a new carb? I wouldn't mind dumping money into this car. She runs incredibly well and looks spectacular for a 19 year old car with 94K miles on her.

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
good.wrench 
Chevytalk Staff
Posts: 20079
good.wrench
Loc: new york,usa
Reg: 03-30-01
Re: 86 Caprice high idle problems
01-31-05 06:25 AM - Post#611015    
    In response to Ronnie Bass

carbs can be a bit complex but nothing to be frightened of unless you have computer elements in yours,if you have them have the carb rebuilt by a professional because you have no way to test them,if you do not have any computer plugs on the carb then rebuilding is weekend project,rebuild kits are available but you must buy a new float as well and theone area of rebuilding that is very critical is the two float positioning adjustments,float level and float drop,the settings and instructions are in the rebuild kit,if you decide to rebuild her get a kit called "hygrade" which is made by blue streak better known as standard motor products from long island city,n.y.it's about the best kit out

good.wrench
c/t staff

84 S-1O 4x4 if your poor your crazy,if your rich your eccentric!


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
01-31-05 07:14 AM - Post#611016    
    In response to good.wrench

I found some Standard Motor Products rebuild kits out there. I'll just go with whatever they suggest for my particular car.

When you say computer components, you mean electrical components of the carb that may be controlled by the ECM? I'm pretty sure the carb is clear of that sorta junk, but I'll be careful to investigate before going forward with any work. I've got some professional mechanics in the family, so I'm sure someone can help me out.

Thanks for the insight! I'll report back when I've made some headway.

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
tripleblack-X 
Member
Posts: 8

Reg: 11-15-04
Re: 86 Caprice high idle problems
02-02-05 11:03 AM - Post#611017    
    In response to Ronnie Bass

Hi!

Just found that link, maybe it helps:
http://www.tocmp.com/manuals/Carbs/index.html

Greetings,
Katharina



 
reybeast 
Member
Posts: 15

Loc: austin tx
Reg: 03-23-04
Re: 86 Caprice high idle problems
03-01-05 12:10 PM - Post#611018    
    In response to tripleblack-X

earlier in this thread, you suggested lubricating the secondary butterfly, what should be used to lubricate it?



 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems
03-07-05 05:48 AM - Post#611019    
    In response to tripleblack-X

I return! But with little in the way of progress. I made a ton of inquiries into different issues with my car since my last post. I've tried different avenues of troubleshooting, and I finally decided to check the codes that are being thrown by the ECM. I got a code 21 and 44 which are Lean Exhaust and malfunctioning Throttle Position Sensor, respectively. I suspect the latter is the cause of the former. First question: would the TPS be a clear cut cause for high idle problems and poor fuel economy. Second question: how easy is it to replace? I've heard from pros and amateurs everything from, "Just buy a new carb" to "rebuild it and learn it." The TPS does require some carb disassembly. Should I just bolt in a new Edelbrock carb and call it as such? Or should I try to rebuild the Rochester Qudrajet that's in there?

Finally, there's a pump in the belt assembly referred to as the AIR pump. AIR is an acronym for something, but it basically provides fresh, pressurized air into the exhaust. What's the purpose of this, and would a malfunctioning pump be cause for the idle issues?

Thanks for all responses. Given the rising price of fuel, I need to get this thing fixed soon. It's getting out of hand.

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
Ronnie Bass 
Member
Posts: 12

Loc: Tampa, FL
Reg: 01-27-05
Re: 86 Caprice high idle problems (FIXED!)
03-14-05 05:18 AM - Post#611020    
    In response to Ronnie Bass

Hey all,

Just wanted everyone to know that after a weekend of carb rebuilding and component replacement, I have a finely tuned automobile! The TPS had 5 different dead spots on it when checking it with an ohmmeter. The idle control solenoid was malfunctioning. I replaced all of the worn gaskets and cleaning out some fouling on the intake and throttle plate. The only problem now is with a code 55 on the ECM (something with the EGR), but that's for another day. Thanks for all of the input and info, guys!

Regards,
Ron

Ron Owner, 1986 Chevy Caprice Classic Tampa, FL


 
Ferruh Tumer 
Forum Newbie
Posts: 1

Reg: 04-08-17
04-08-17 02:55 AM - Post#2685552    
    In response to Ronnie Bass

Ronnie,
Thanks for this post. I have 86 Caprice and have the exact same problem. Even the yellow engine check signal that appearance randomly, it is the same problem that I have. The worst thing for me is that because of that high idle, transmission kicks when I put it from P to R or N to D or R... The idle screw does not help to reduce the idle at all.
It has been a long time since your post and hope you can read this and reply. After all that then, would you suggest to replace then the TPS and the idle sensor?
Thanks a lot in advance.
Ferruh



 




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