Chrysler Repair: 99 caravan 3.0L stumbles runs hot, cam sprockets, freeway speeds

Question
I have a 1999 dodge caravan I bought it had a exhaust leak and ran poorly I did a complete tune up at 109k plugs wires cap rotor no change. The van still stumbled badley just off idle surged at freeway speeds and would backfire through the intake. I took it to a shop to have the cat and egr checked all good scanned system nothing wrong o2 sensor says rich. Replaced o2 sensor exhaust manifold and no change same symptoms replaced egr valve tps sensor exhaust manifold cracks again (new one). Put in new timing belt water pum and tensioner no change.  New fuel pump and filter nothing coil distributor again nothing just the same engine has 22 hg vacum and has 165 psi compression across the board give or take about 2 psi max but it is a very noticable problem and uses a lot of fuel (my 1 ton chevy gets better mpg). I don't get the problem no lifter noise good clean oil idles smooth has more power when you floor it seems to run worse when cold. Absolutly no codes. I have also replaced many of the relays and probely more parts I cnat think of right now the van has 112k very clean adult owned but clearly a jiffy lube repair special.   Please point me in the right direction. I have purchased new injectors to do next but don't think it is the problem.  I couuld have bought a newer van with less miles help. Thanks

Answer
Hi Nehl,
In thinking about what sort of things can be wrong but not set a code, the only item (other than the ones you already replaced) is that the MAP sensor is inaccurate but not so badly as to set a code. I have had that experience. So consider replacing that sensor and see if the mixture might be improved, and end this situation. I wish I could suggest other things. I assume that you checked that the timing marks on the cam sprockets are lined up. If I can identify another possibility I will certainly let you know. You didn't specify what you meant by ' runs hot', but the thermostat may be not fully opening. Then you could also check that the coolant temp sensor when the engine is warmed up should show a reading of 700-1,000 ohms across its terminals as that too will affect the mixture if inaccurate. It is located next to the thermostat housing. And of course keep checking for codes. When you replaced the distributor did you also change the plug wires as those could be arcing, along with the cap and rotor?
Roland
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