DoktorC

My father just bought an '88 coupe with 200,000kms. The old owner stated that he couldn't get it to pass an emision test (required here in Ontario). I drove it home and it runs well..pulls hard..but it idles alittle high 1200 rpm+/- and alittle surge. The idle drops significantly in gear, almost to the point of stalling but then the ecm bumps it and it's fine...put it in park and it revs alittle then settles down to the 1200 but its not steady.

I don't see any CEL or service engine light...I just don't really know where to start. This is "our" first C4 after many C3's so we don't really know the ins and outs of this fuel/emision control system.

Any guidance would be greatly appreciated!!!

Thanks!

rick lambert

Well, as a base line you should start off with a good tune, maybe even clean the IAC=Idle Air Control, I'd run some SeaFoam through it, change
all filters and oil. Your SES light isn't flashing is it, that would represent a code. I suggest you get the FSMs or Helms manuals for year specific-our C4s are not what you're used to working on-I've had 2 others, a 62 and 64...you need the factory service manuals.

highpockets

Does the SES light self check(light up briefly) when starting the car ? Several times,I have seen cars with problems were "fixed" by removing the bulb. Start there,check all obvious things,report back. good luck

DoktorC

I really don't think the SES is lighting!!! I didn't know where to look when we were actually looking at the car (like an idiot!!). I'm used to the SES to be in the gauge cluster..and I wasn't 100% on what lights this thing was supposed to have being that it's from 1988 lol.

I'll check the bulb and then see if I can get it to throw a code.

The oil is clean and it has what appears to be a brand new K&N in it. I was planning on cleaning the throttle body and MAS (that is a MAS between the thottle body and filter right?)

You'll have to forgive my ignorance...all my GM experience is with carbs...I do have a mildly modded Talon so I (VERY) used to working on cars lol but like I said I don't really know how this system works...but I'm sure I will shortly.

Rick - the first purchase will be a manual...I just like to hear the voice of experience so I know where to look.

Thanks guys!! Great info.

tequilaboy

The factory main cat on my 88 burned up and blew out sometime back around 1992. After it blows you can see straight through the cat.

I can't imagine one lasting this long.

AGENT 86

Sounds like there is a vacuum leak somewhere. Reset the TPS and min idle and then start looking for a leak if idle didn't settle down.
https://www.corvetteforum.com/techti...D=55&TopicID=2
I have my manual on my hard drive. If you want some specific info just give me a shout.

RRT vette

The SES light should come on the DIC when you turn the ignition on but don't crank. If not, then I would check the bulb. As for the high idle, Agent 86 gave a good suggestion and look for vacuum leaks. Does it idle better when in closed loop or operating temp?

DoktorC

It seemed to be better in closed loop. I didn't really notice an issue until I got down the road. I'm going to help my Dad with the car today so hopefully I'll have some answers this evening. I'll start with a general check over; looking for vaccum leaks and the SES light. Then I'll do the throttle body clean and IAS/TPS setup. I'm sure that will improve the idle condition and hopefully the SES will give some indication of the emissions problem.

SunCr

If the emissions failure is because it was spewing too many HC's or the the CO level was off the chart, then you should look for anything that would trick the Oxygen Sensor into thinking it was lean. Vacuum leaks are a good place to start - also the intake - air pump system (clamp off the hoses to the headers) - the headers themselves - or basically anything that might let air into the engine after the MAF.

88BlackZ-51

Hi, I am near by in Barrie Ont with an 88. I had a little prob with my emmissions at stock timing, then bumped it down to base timing (0), and it passed with flying colours.

Are you interested in coming to the track with us, or you just cruise?

The car you bought, Was it the one that was forsale in the supershopper for ever? You should stop by sometime with the car.....

DoktorC

Well it turns out there was no bulb in the SES so I figured we had it solved...installed the light..turns on for the check and goes off when I start it lol. Now, I believe the battery was unhooked until we showed up to look at it so we may not have enough time on it to actually throw a code. I know my car takes awhile for the O2 sensor to trigger the CEL after I reset it. I don't see any vaccum leaks but my dad is going to spend the day with it tomorrow. He's going to do a full "tune-up" so he knows he's got a good starting point. I must say the car runs really well...gets all sideways in 2nd..I miss RWD!!

88 - Yes this is the one in the supershopper lol. The guy couldn't get it to pass and didn't know what to do. We got it for what I think is a steal!! Anyways, it's actually my Dad's car so I doubt I'll have the opportunity to run the car much but I do appreciate the offer!! Do you know anyone with a logger??? I could maybe use a quick scan to see where I am with this thing.

DoktorC

Well, he found a chewed (literally) vaccum line that runs from the EGR to the canister...which, according to the manual controls the EGR valve. I would think that this would be a main contributor to the emission issues!! The throttle body was also really really dirty so that was a great suggestion. He's just waiting on new gaskets and we'll reset the TPS and ICS.

Thanks again for the advice..hopefully it will pass!!!

91quasarblue

Hello I have a 91 that didnt pass emiss this april. Last summer I did the tune up and whole nine yards it turned out to be the brake booster it was cracked and had a bad vacuum hopefully that chewed vac line is your problem.I had the rough idle and all that stuff and when the mechanic changed the booster the idle was better and passed the emiss test with flying colors.

rick lambert

Thanks 91, we need to hear feed back like that. you to Doktor

DoktorC

****Update****

It didn't pass!! Tech guys says it looks like it's running rich (even though there's no visible signs). It's the worst at idle....There are no codes showing and the car seems to run very well and no rattles from the cats. I looked at the ECM to see if I could tell if it's been out and chipped but I don't see any evidence that it's been out of the car. Will a chipped car pass? What am I missing?

HELP!!

RRT vette

DoktorC, I would follow SunCr's advise again and double check vacuum leaks. As Rick Lambert and I discussed, these cars have a ton of vacuums. I just found a leak the size of a pencil that I had looked for for a while. Bummer, you didn't pass.

SunCr

AND - you might post the actual test results for a little more insight.

ED HEISER

I just had my brake power booster changed today on my 88, it made all the difference in the world at idle, much better brakes too! Also changed to 20-50 oil with an additive after a seafoam smoke out. No more excessive blow by which was screwing with the computer. I guess my piston oil rings were all carboned up in addition to the booster leak.

Red C4

Just did my 150,000 mile '91 here in Ontario. Would not pass the first time . Seafoamed it and also found a couple of cracked vacuum lines and a cracked Distributor.
Runs smooth now and passed easily.
Check Vacuum lines,plugs and wires,distributor cap . It's the small things quite often .

R88Vette

I had my car fail with the O2 sensor stuck between rich and lean. No diagnostic code, but, not switching rich/lean/rich. You can detect this if you plug into the OBD I and scan the car looiing for O2 crossings.

Fixed this problem by replacing the O2 sensor. I used a heated O2 as my car has headers which kept the sensor from heating up.

Good Luck!