BEAU-SOF

symptoms. at idle, interior dash and headlights flickers based on the idle(Ex: low idle(500+ which usually happens lights flicker. idle at say 700 no flicker), using power windows seems to drain.

I've researched this and I am pretty sure its the alternator but I just want to make 100% sure because I do not wish to start replacing parts that may not need replacing. power wise it seems fine. battery voltage doesn't seem to dip once started and idles but this is based on guage.

starting. it cranks no problem but cold start is definitely hard. although I am suspecting this is a separate issue here.

this is a lot more of a annoyance than a major problem but I have a lil extra cash and wish to fix this. any help is appreciated.

thanks

John A. Marker

Do you have under drive pulleys on the engine? 500 RPM seems a little low for idle.

BEAU-SOF

Honestly I do not know. I bought the vette from a vette dealer in april. I do know the engine was replaced with a gm goodwrench about 27k miles ago. based on the previous owners notes and logs I do not see underdrive pullies installed.

ive had this idle issue since ive owned it.. I am not sure if its a separate issue or bad alternator. I've read low idle is a symptom.

ynot d

Check the alternator output with a DVO meter. It should read 13.5 to 14.5v when measured across the battery terminals at idle. DVO set on DC volts.

BEAU-SOF

Welp just came back from Pep Boys. Good news and Crappy news..

Good news.. confirmed its not the battery or alternator

Crappy news... confirmed it is an electrical issue.

just my luck considering battery and alternator are simple fixes...

the manager then recommended I goto JD Corvettes which is the exact place I goto anyways. in which they told me if the car has good power and runs decent then save that electrical issue for last when restoring because chasing down an electrical issue can get pricey real fast.

good advise..

thanks guys for the help.. Have a safe holidays!!!

ToniJ1960

That does sound like a little low idle speed, how does it act if you gas it enough to bring it up to 600 or 700 and try to activate some loads? Do the lights dim?

BEAU-SOF

No the lights do not dim when I rev it to about 700-800 rpms.. I play the radio I mess with the windows door locks but I have never cycled the headlights on and off to see..


but no I do not notice the lights dim under your proposed scenario..

ToniJ1960

I wouldnt think theres anything electrical to worry about. It sounds like the regulator is working ok so the alternator must be ok too I think.

Im just learning about these cars but why would the idle be so low?

nobodycls

Is this the 85 listed in your profile? Does the car maintain the same idle speed when turning on lots of electrical loads(headlights, blower motor, rear defroster, etc.), or when turning on a/c, or going from park to drive? The ecm controls idle speed with the IAC, and will aim for anywhere between 550 to 750 and sometimes higher depending on conditions. What is the idle speed at cold startup? Also, what does the idle speed do at warm startup? This kind of info will help the guys here help you narrow down any problems. It does sound kind of like fixing the idle issue will solve the other problems you explained.

BEAU-SOF

I do not think the a/c is connected... lights on radio on, at idle it seems to remain steady at 500-550 it dips only slightly to 450 when coming to a full stop.. however the light flicker is noticeable

nobodycls

What does the idle rpm do when going from park to drive?

nobodycls

Sorry, I think I made an edit after you read my first post. What exactly does the idle rpm do at cold startup and at warm startup?

BEAU-SOF

I'll answer both questions. in drive it idles between 500-600 rpms... in park 600-700 rpms..

cold start 600-800 then once it hits 100 degrees on the gauge it jumps to 700-900.. then once warmed up it dips back to drive rpm mentioned.

yes 85 corvette..

thank you for your input btw

nobodycls

At warm startup, does the idle speed flare up high for a second or two, then drop to 500-600 rpms? CEL on? any codes?

DinoBob

Check the terminal block behind the battery. Make sure all the connections are tight and that the block is in good shape.

Cliff Harris

Your cold start RPM sounds low. You might have dirty IAC passages in your throttle body. Another possibility is that the TPS is not adjusted correctly. You might have a bad coolant temperature sensor. A minimum idle adjustment would probably be a good idea:

http://forums.corvetteforum.com/1570563689-post1.html

The ECM adjusts the RPM based on the startup coolant temperature. If the car is -40° then the ECM is programmed to idle at 1200 RPM. My car idles at about 900 RPM in Park when cold (that's Southern California cold -- it was in the 70s today).

[ EDIT ] On further thought, I think your CTS (Coolant Temperature Sensor) has a problem, either the sensor itself, the connector pins might be corroded or you might have a broken wire. This is the CTS on the front of the intake manifold. If the ECM thinks the engine is hot it will set the idle to a low RPM. [ /EDIT ]