Wierd issue that effects startup and Idle

We've got a 1998 Honda Passport in the shop and we can't seem to trace down this issue. I rarely deal with Honda's so I am not to fimilar with them, hoping one of you can help me out.

First off the big problem is it is hard to start, and I mean extended crank times (usually 5 seconds plus before it will fire up and kind of cough at first). Then while it is idling the interior lights, headlights and all lights flicker slightly. Obviously we've tested the battery and alternator and everything was good. But, the wierd part was during testing the alternator I could not get the car to hold at 1500 RPM's, NO MATTER WHAT! It would get there and just climb or jump back down to idle.

Now at first the map sensor had some funny reading on the scan tool from the MAP sensor (showing BARO reading of 26 with key on engine off) replaced the map and the reading went back to normal. Then after further inspection the IAC was gummed, and I mean gummed it would not move at all. Replaced that and the problem still persists. Seems to me like a CKP issue but it never dies just runs rough a little sometimes. Maybe possibly a fuel issue (filter or injectors clogged) but I'm doubting it considering the STFT and LTFT's are subtracting fuel at idle.

Anyone got any ideas?

Plugged EGR and or PCV and or EGR tube (easy to clean with carb cleaner).

Intake manifold gasket broken (very common)

Weak alternator under load (Isuzu's do funny things with weak electical systems)

check out:

http://isuzufaq.ibctech.ca

for a bunch of info on the above issues.....

First off, it's not a Honda. It's an Isuzu. Not a single part on that truck made by Honda. Well, maybe the badges but they were probably subbed out and made in China.

I would be checking the fuel pressure to see if it's bleeding off when it's not running. If it is, I somewhat recall some sort of check valve in the tank that can be defective or maybe leaky fuel injectors. Did you check the TPS readings? Does the TPS output voltage vary smoothly from closed to open throttle? Also, like Amigo-2K said, check for leaky lower intake gaskets.

Also, the alternator seems bad to me. There more to an alternator test than measuring output voltage at 1500rpm's. If the current is fluctuating at idle, a voltage test won't reveal that.

First off, it's not a Honda. It's an Isuzu. Not a single part on that truck made by Honda. Well, maybe the badges but they were probably subbed out and made in China.

I would be checking the fuel pressure to see if it's bleeding off when it's not running. If it is, I somewhat recall some sort of check valve in the tank that can be defective or maybe leaky fuel injectors. Did you check the TPS readings? Does the TPS output voltage vary smoothly from closed to open throttle? Also, like Amigo-2K said, check for leaky lower intake gaskets.

Also, the alternator seems bad to me. There more to an alternator test than measuring output voltage at 1500rpm's. If the current is fluctuating at idle, a voltage test won't reveal that.

Alternator seems to be working perfectly at idle it had steady voltage (don't remember exact number but it was fine). We dont have a lap scope (got one on order) but with a multimeter TPS sweep test everything looked good, no spikes or drops.

With all the issues to me it seems like all of them could be explained away with a block ground loose, but they all seem fine. It's very possibly that it is an intake gasket, we further check that today if we really can.

We are a small school, I just recently began teaching here and if we had everything we needed this thing would have been done already but we've only got 1 genesis scan tool that is terrible and has no function tests. But due to budget issues we are forced to do it blind.

pick up a used factory alt of ebay or drive to a pick and pull near you and get one.

Alternator seems to be working perfectly at idle it had steady voltage (don't remember exact number but it was fine).

I have heard that you should also check the alternator voltage with the multimeter set to AC. It should read zero, if it does not it indicates a defective rectifier.

'99

You want to be checking current output. Voltage can be rock steady but current could be all over the place. A varying current will cause lights to flicker.