playsdixie

removed the smog, egr crap , installed headers/ roller rockers..had it dyno'd....
engine runs great with one exception....on initial start it takes a minute or two to run smooth...purrs like a kitten when warm....since I live in s fl...it's not a big problem...any thoughts on what it could be? new everything above the block....idle wavers....just a couple of minutes....then steady at
650 ,,,,any thoughts would be appreciated....Iac valve is new...Paul

S S0DEN

I removed the Air but left the EGR and mine does the same thing. I could be wrong, but your idle seems a little low. Mine idles at 8-9 and 10-11 when cold.

playsdixie

650 in drive..local corvette guru here wasn't sure either....I was thinking it had someting to do with the headers/ air flow......no cats...just a couple of cherry bombs at the x pipe...air is ripping out..not a bad sound either.
the stock engine ran/started perfect...but I made so many changes..bigger tb/ manifold plenum from an 86 . rail too....not too big a deal...clears up in seconds....helps to restart.....paul

DanielRicany

You may need a tune. The computer can handle bolt ons pretty well but when you change the cam you need a tune. You didn't change the cam, but you did add roller rockers, I'd imagine 1.52 or 1.6 instead of the stock 1.5 ratio.

If you did go with 1.6, that could be the reason why it runs like crap until it gets into closed loop.

playsdixie

they were 1.6 engine set up now is from the dyno last week....haven't made any adjustment yet....guess I'll check the iac this week end...put a new one in last year...

leesvet

A computer controlled engine won't run right when you remove a BUNCH of things that ARE part of the "tune" program that the car came with.

This ain;t your granddads Oldsmobile......

Your basically stock engine can get by with a "tune by phone" or mail order tune...just contact the tuner shop, tell them EXACTLY whats been done and they will burn a prom to fit your engine. That prom is useless anywhere else. A "tune" is custom. Mail order is about $250-$350. A real performance tune will run ya about $750...
Until you get a program in the ECM that's aware of the changes...its gonna stumble, cough or gag under some conditions.
Its just not gonna be "right". If its OBD-II you have to take it in OR YOU can buy the stuff to plug in with a lap-top and get the program and make changes yourself...



ANY time ANY intake or a major exhaust change is made, that warrants a new "tune". Most EFI cars will get by with the same tune for some minor changes because the stock tune has some wide parameters, but multiple changes or d/c under the hood require the tune to be updated otherwise the ECM thinks the engine is still stock and treats it that way...except its getting **** poor data from sensors that are telling the ECM something is not right...it just cannot tell what or do anything about it. If mechanical changes take place the ECM will be effected but it can't do much about it...unless its got the right "tune" or picture of what things should look like.

You might call Jon too. All those changes also warrant new upgrade injectors. Whats another $300? Just do THAT before you do the tune....

If you are not going to tune the engine, don't remove the EGR. The EGR can be taken out of the "tune" but you're asking for trouble by removing the EGR and failing to delete it in the ECM.
All these 'mods' CAN cause serious knocking under certain conditions.....the ECM is looking for the EGR to quash the excess combustion temp that causes severe knock and/or ping with a brief timing retard and a taste of cold gas to cool the combustion...EGR is not a bad thing...but many people think it robs a bunch of performance. It does NOT. If anything, it can save the engine from knocking to death.
Be sure to get EGR deleted out of the new tune. If the tune is 'right' there will not be any knocking issues.


BTW...
the "low idle..." 650 IS normal. An engine that's idling at 800+ when warm is a sick engine. Vac leak, IAC issues, injectors, Ign timing AFU. Sumthin ain;t right.
Idle that high is hard on an auto tranny and bad for a stick as well...if the clutch drags ANY at all, grinding we go...
Cold idle @ 900-1000 is common. Briefly !
1100 for a few seconds at cold start...not unusual BUT, if it has not dropped to 650-700max after it hits 150* or more...something is wrong. Temp sensors, air leaks, all contribute. There are around 2 steps the ECM goes thru regarding idle from cold start...

it will drop it when it hits a magic temp that wakes up the O2 sensor,
(126 exactly on mine) and again as it passes the 150s and approaches the "normal" operating temp range of 180+.
It gets 'in' CL as the O2 inputs and the temp sensor data is what the 'tune' is expecting.

IAC...
YOU don't adjust the IAC. The ECM does that. That's part of the "tune".

A 'tune' is simply a program for THAT pile of parts. Without the correct tune there will be issues that YOU cannot sort out. Whenever parts change,. the "tune" (program) must change as well. Welcome to EFI.

playsdixie

great stuff..thank you so much.....just paid 700 for the tune to get the egr/air deleted....car runs and performs great with this one little exception for a minunte at start...considered the iac due to the fact it runs a little better if you shut it off and restart it immediately....paul

WW7

This is just a (WAG), but did they tune just the closed loop operation??
Our cars run off a set of perameters in the ecm chip set for a stock engine while in open loop..Once the car goes into closed loop it starts getting feedback from sensors to correct for any air / fuel differences. If your open loop operation is still stock, and your running a modified engine, it would definitely cause it to run funky, or maybe your open loop tuning needs more work......Someone please correct me if my thinking is wrong on this........WW

ghoastrider1

just wondering if you got the collectors with the O2 sensor bung? BTW, whats it dyno out? B4 and after numbers? I am in the middle of these changes on my 86.

S S0DEN

In adjusting the TPS correctly, I was told my normal idle should not dip below 700 RPM's having the standard and the 700R4 version is 600-650RPM.

My car prior to the TPS adjustment sputtered on WOT and idled below 600 RPM's - This morning I warmed it up, 1000 RPMs cold then after a few minutes it kicked down to 700 RPMs. Drove for 3 miles and at the light, with the clutch depressed - 800 RPM's, if I sit for more then 30 seconds, it will drop back to 700 RPM's.

I do know my Throttle body is worn, I have had issues with the throttle being hard to open and have had to lube it (non silicone spray).

I removed my AIR system a long time ago and gutted both cats. I am waiting on my new exhaust and ported intake in the mail. I left the EGR functional.

I am sure the Tach is not 100% accurate, so it may be in the 650-750 range.

QCVette

Those are my thoughts too.

I had an '85 that had minor mods to it. It would run fine when warm, but it would hesitate and bog when it was cold. I pulled off a couple of mods and it ran fine again. I got an SLP chip for it and then I could put the mods back on and it ran fine again both when it was warm or cold.

Good luck.

Rohn

With headers and NB02 in the collector a heated 02 sensor is nearly mandatory...

WW7

The OP is having his trouble in "Open Loop" within the first few seconds of starting the engine , the O2 sensor isn't operating until the engine warms and goes into Closed Loop.....WW

playsdixie

I think your on the right track...going to see the tune guy tomorrow...
I was leaning to a faulty aic valve.....thought it might not be seating correctly.....thanks for all the input....if I solve it, I'lll let everyone know...
Paul

WW7

Paul, you may want to invest in a scanner in the future...Scanners work great to let you know what is , and what isn't , working correctly on your car..I use mine alot on the Vette....They really help you narrow down problems , and you can pick a decent one up for a few hundred dollars..If you get one that does both OBD1 and OBD2 , you can use it on all your cars...Just a thought.....WW

gerardvg

Standard when started cold the rpm will go to around 1,200 rpm for a few moments and settle to around 600 rpm, when hot the idle will be around 580 rpm. (With tunerpro and a a moates ostrich the idle speed can be changed, as well as deleting EGR and removing the EGR diagnostic check otherwise you will get EGR codes on the highway after 15 mins or so) however my 85 cpu has the idle speed at 580 with temperature idle offset, that is why it will vary as the temperature changes. However the idle will be stable.

I have had my egr disconnected for many years, no pinging/knocking.
The one main thing you should do with any change is set the base idle again. The ecm expects the throttle body and throttle position sensor and timing etc to be correct, and changes will cause the engine management chase its tail.

Below is the steps to set your base idle.

First thing to do is disconnect and re-connect your ecm wire near the battery (or disconnect the battery) as the ecm will detect faults and make adjustments to try and rectify them. ie retard timing.

Set your car to a base idle (as per my shop manual)
WHEN HOT.

Connect a paper clip, to your diagnostic terminal under your dash connect to terminal A and B (the top right two pins).
Turn on ignition but don't run the engine.
wait at least 30 seconds and then remove the idle air valve connector (IAC) (the square plug) then turn of ignition and unplug the paperclip.
Now remove the timing connector a single wire near the fuel pump relay.
Start your vette and set the idle speed to 400 rpm in neutral (auto trans) 450 rpm (manual trans) then check your throttle position sensor,
the top two wires it should be set to 0.54volts dc, also confirm with engine off that the tps rises to 4.5 volts at full throttle.
Turn of the ignition and reconnect the iac valve connector and timing connecter and start your vette.
it should go to 1200 rpm then drop slowly to 600 rpm, take the car for a 15 minute drive with the usual stop lights.
It is normal for a little hunting while the ecm relearns.
All should settle after 15 to 30 mins normal driving and have a stable idle.
Of course any vacuum leaks fouled plugs can affect the correct base idle.

Rohn

Very true. However that does not discount the value of a heated NB 02sensor.

As we know IAC position is dependent on coolant temp. Initial startup postion may be timing out to quickly. There is a delta filter I believe for that. A change there may allow high idle a bit longer.

playsdixie

it's not just the idle that's the problem...it's actually getting it fired up...use to fire immediately...if it was carburated, i'd be wanting to pump the gas.takes a few cranks and restarts.....it's a relatively new I A C valve..six months...not a lot of miles on it..once started, idle will waver until 145 degress..then smooth...starts beautifully after that....going to have the dyno tune guy take another shot at it next week....

Rohn

Needs more cranking fuel. Unfortunately it needs to be done on a cold engine. Once at dyno engine will be warm. I added more to my car due to changed in intake plenum and runner volume(TBI) and reduced crank vacuum(cam). I added 10% more several times until I hit the right balance.

playsdixie

first....how do you do that?

second...I was told that the 22# injectors needed 43 lbs....they are running it at 32 for the dyno....I think it should be higher...might make a difference at start.